TEE PUBLICATION OF THIS B S B a B C H WAS FINANCBD IN P U T BY CARLOS F. MACDONALD RSSEARCH FUND” “Tax DOWB ERUPTION AND DECAY OF’ THE PERMANENT TEETH I N PRIMATES ADOLPH H. SCHULTZ Laboratory of P h y k a l Anthropology, Johns Hopkind University TWENTY-ONE MQUBES INTRODUCTION Comparative investigations on the morphology of the teeth in primates are much more numerous and extensive than are studies dealing with the eruption, wear, decay, and loss of the teeth. I t is the purpose of this paper to contribute new data on what may be termed the life history of the teeth of primates. Information on this subject is very much needed in order to demonstrate t o what extent eruption and decay of the human dentition follows the rules prevailing among primates in general and how far the conditions in man may have become altered in response to human specializations. The writer’s interest in these problems started many pears ago during his earlier comparative studies on the growth of primates, when it became necessary to estimate the relative or physiological age of monkeys and apes. Such age estimations are based in part upon the state of eruption or upon the degree of wear of the teeth. It soon became evident that the reliability of conclusions in regard to age from even the most careful examinations of the dentition must remain very limited until we are in a position to make fewer assumptions and, instead, actually know more about the relative age and sequence of eruption of the teeth in different types of primates. 489 AMERICAN JOUBNAL O F PHYSICAL ANTHROPOLOGY, VOL. XIS, NO. 4 JANUABY-MARCH, 1035 490 IIl)OLPH H. SCHULTZ Facts for the solution of these problems can be gathered chiefly from two sources : periodically repeated examinations of the teeth of living primates and observations on the teeth of large series of dead specimens of differing ages. Both these sources were utilized by the author, but opportunities f o r dental examinations on living monkeys and apes are scarce and the study of dead material is limited by the fact that most collections contain relatively few skulls of juvenile primates. For these reasons, as well as on account of the very marked variability of some phases of tooth eruption, the observations recorded in this paper are at times only fragmentary and in part permit merely tentative conclusions. This study started with and emphasizes the collection of new data bearing upon the relative ages and the sequence of eruption of the permanent teeth in different primates. Material for a corresponding study on the deciduous teeth is not yet available in a sufficiently large amount to justify more than a few preliminary and generalized statements. During his examinations of various collections of skulls of monkeys and apes, the author has recorded all deviations from the usual and normal condition, i.e., all cases of variations in the number and, position of teeth and all instances of pathological changes in the teeth and the alveolar processes. These data are in a sense a mere by-product of this study and are presented, without going into many details, as a basis for the evaluation of the corresponding conditions in man and in order to complete the picture of the fate of the teeth during the lives of their simian owners. This investigation does not extend to the sub-order of the prosimians because the accessible material is too scanty, particularly in regard to juvenile specimens, for the establishment of representative averages. In an attempt to recognize and demonstrate the role of a simian heritage in the life cycle of man’s teeth, this exclusion of all Lemuroidea is a negligible factor because these primitive primates are unquestionably far removed from that part of the entire primate family tree to which man must be assigned. ERUPTION AND DECAY OF TEETH IN PRIMATES 491 The literature on the eruption, irregularities and decay of teeth in primates has been consulted and is quoted wherever comparisons with the author’s findings seemed desirable. It will be noted that, unfortunately, there exists a considerable number of more or less significant disagreements between the writer’s results and those of some other investigators; these will be discussed in their proper places, though in some few instances it is impossible to suggest any possible cause f o r such discrepancies beyond the general statement that in the study of eruption of teeth one deals with a variable process and that the frequency of diseased teeth can apparently differ within wide limits in different groups of the same primate genus or even species. All the new data obtained by the writer are presented in such a manner that future investigators of additional material will be able to combine their observations with those recorded here and thereby will be in a position to base their new conclusions upon more ample evidence. Certain reports on primate teeth could not be utilized, because their authors failed to state whether the particular conditions discussed had been observed in one or in a great many cases, so that it cannot be decided whether they were describing possible exceptions or well-founded rules. MATERIAL The new data regarding the absolute ages of eruption of the permanent teeth are chiefly based upon t.he author’s observations on the growth of ten living rhesus macaques, born in the Carnegie colony of these monkeys, and of two living chimpanzees, kept at the Department of Anatomy of the Johns Hopkins University. The author is greatly indebted to Dr. G. L. Streeter and Dr. C. G. Hartman for having been given the rare opportunity to follow the growth of these macaques of known ages. These studies will be continued until more animals have acquired thetr full permanent dentition; data on tooth eruption in these macaques, appertaining to a shorter average period of growth, have been published by the author (’33) in a previous report. 492 ADOLPH H. SCHULTZ In addition, it has been possible to make a few scattered observations on the age intervals between different phases of the dentition in various living primates, examined repeatedly at different times, and on the state of the dentition in a few other primates of actually known age. F o r these opportunities the writer is indebted chiefly to Dr. H. Fox of TABLE 1 List of primate skulls emmined in the direrent eollectiona YUSLEY DOXPABA TNX ZaOaLWY HdRVABD u. 8. BIOYUSXUY aOGIOAI SUEVZY COLLEGZ Gorilla Pm Pongo Hylobates 50 31 75 135 Pithecus Papio Lasiopyga Colobus Nasslis Pygathrix 237 52 201 61 43 316 Ateles &bus Alouatta Saimiri Oedioomidas Total= I 32 52 70 18 17 1390 .. 259 108 17 16 .. .. .. .. 12 36 1 10 5 16 .. .. .. .. .. 10 94 .. 492 38 .. I .. .. 4 8 .. .. .. .. .. .. .. .. .. .. 26 19 39 .. 3.. 8' .. PHYSICAL ANTEEOPOUXIY ABOMTOBY HOPXIrr8 UNIVERSITY :OLLXCTION A E. SCHULTZ TOTAL 12 28' 1 6 ' 2 7 2 13 323 212 95 170 60 11 6 233 24 26 3 1 3 542 123 234 74 48 336 1 10 141 71 169 53 10 757 200 156 286 71 38 2908 .. .. .. .. 1' 137 .. 'Including 15 specimens loaned by Field Museum, Chicago. Including some young embalmed specimens. the Zoological Park in Philadelphia and to-Dr. W. M. Mann of the National Zoological Park in Washington. The largest part of the data to be discussed are based upon the examination of the dentitions of the skdls of primates in the collections listed in table 1. For having been permitted to study the primate material in the different museums the author wishes to express his sincere gratitude to Mr. G. S. Miller, Jr., Prof. T. W. Todd, Mr. H. H. T. Jackson, and ERUPTION AND DECAY OF TEETH IN PRIMATES 493 Mr. H. J. Coolidge, Jr. The enormous and splendid collection of skulls of wild gorillas and chimpanzees in the Hamann Museum of Anatomy and Comparative Anthropology proved to be of particular value for these investigations, since it contains such large numbers of specimens with incompletely erupted dentitions, as well as of really old specimens. The names of the genera of the primates in table 1, as well as the names of the species mentioned in the text, follow consistently the convenient and well-known review by Elliot ('13). The first four genera in table 1 represent the higher primates which are unquestionably much more closely related to man than any of the lower forms. The genus Symphalangus has not been included, because no sufficiently large series of skulls of particularly young animals could be obtained. The following six genera are Old World monkeys, the first three belonging to the subfamily Lasiopyginae and the last three to the subfamily Colobinae. The last five genera in table 1 are New World monkeys which are distinguished from those of the Old World by possessing three, instead of only two, permanent Premolars on each side of each jaw. The last genus (Oedipomidas) belongs to the family Callithrichidae which is characterized by the lack of third permanent Molars. The total number of 2908 primate skulls examined contains 2394 wild specimens, killed in their native habitat, and 514 captive specimens which had lived for varying and in most cases unrecorded periods under more or less suitable conditions in captivity. All these skulls possessed at least two of the permanent teeth, the comparatively few younger specimens in the collections having been omitted in this report. The permanent dentition is incomplete, or even the last teeth are not fully erupted, in 982 skulls of which 587 are wild and 395 captive specimens. This is the material used for the study of the sequence of eruption of the permanent teeth. Among the remaining 1926 skulls, in all of which the permanent dentition is completely erupted, there are only 119 captive, whereas 1807 wild specimens. 494 ADOLPH H. SCHULTZ EXPLANATIONS It is necessary to define the exact meaning of some of the terms, as used in this paper. In most instances considerable time elapses between the first appearance of a permanent tooth and completed eruption, as indicated by accomplished occlusion. In living or in embalmed primates a tooth is recorded as erupting not when merely the first, small, white tip of a cusp appears through the gum, but rather when the entire top of the crown has just pierced the gum, though the tooth is still far from functioning by meeting its antagonist in the other jaw. In the skulls of primates a tooth is considered to be erupting when the uppermost portion of its crown reaches clearly above and not merely to the alveolar margin. In many juvenile skulls one or more permanent Premolars can be seen underneath the corresponding deciduous molars which are evidently almost ready to drop out. Even though a Premolar actually projects above the alveolar margin, it is not counted as an erupting tooth until the deciduous molar to be replaced has definitely lost its hold by even the last of its roots. In the relatively few cases in which the right and the left halves of the jaws differ significantly in regard to the state of eruption of the teeth, the side with the more advanced condition is utilized for recording. The state of attrition of the teeth has been noted on each skull and it was found that it suffices for the present purposes to divide the various degrees of attrition into only two general classes, designated as ‘slight’ and ‘much.’ All cases in which the degrees of attrition of the permanent teeth range from no macroscopically visible signs of wear to at most very moderate wearing of the crowns of usually only the first Molars, Incisors and Canines are placed in the group of skulls with slight attrition. As soon as more than the just-mentioned teeth bear readily noticeable signs of advanced attrition, accompanied by at least partial exposure of the dentine, the cases are included in the group with much wear of the teeth. This, as most classifications, is somewhat arbitrary, since a small percentage of the specimens could with equal right be assigned to either of the two classes. Only after ERUPTION AND DECAY OF TEETH I N PRIMATES 495 considerable experience is the observer in a position to make consistent decisions in all cases in which there is any doubt regarding the degree of attrition. For this reason the writer reclassified his first 260 records after all the other material had been examined, changing ‘much’ to ‘slight’ wear in eighteen cases. The primate skulls have been divided into three age classes : ‘young,’ ‘adult’ and ‘old.’ All skulls with permanent dentition started, but not completed (including cases in which all permanent teeth have appeared, but not all completely erupted), are classified as ‘young,’ all those with completed eruption of all teeth and with open base suture (synchondrosis spheno-occipitalis), or closed base suture, but only slight attrition of the teeth, are classified as ‘adult,’ and all those with completed dentition, closed base suture, and much wear of the teeth are classified as ‘old.’ For the purpose of this study, a suture is considered to be closed if at least threefourths of its entire extent have become obliterated on the ectocranial surface. In order to save space, particularly in the tables, the following abbreviations have been adopted in this paper: The names of deciduous teeth begin with small letters and those of permanent teeth with capital letters, thus avoiding endless repetition of the words ‘deciduous’ and ‘permanent’ (except a t the beginning of a sentence). In the dental formulae only the initial letters of the names of particular teeth are given and those of the upper jaw stand above the horizontal line, whereas those of the lower jaw below this line. In the text the names of the general types of teeth (e.g., Premolars) are not abbreviated, but wherever the name of a specific tooth (e.g., second Premolar) is mentioned it is abbreviated according to the following list: Deeiduour 168th medial incisor = il lateral incisor = i2 canine = c firat molar = m l second molar = m2 Pmmanent taeth medial Incisor = I1 lateral Incisor = I2 Canine = C first Premolar = P1 second Premolar = P2 first Molar = M1 second Molar = M2 third Molar = Ed3 Appertaining to upper jaw = u. Appertaining to lower jaw = 1. Wild specimen = w. Captive specimen = c. 496 ADOLPH H. SCHULTZ AGE OF ERUPTION OF TEETH Deciduous dentition The ages of eruption of the deciduous teeth in primates with known date of birth have been recorded in very few instances. As far as the author can ascertain, these ages are unknown in all the lower primates, except the macaque and one New World monkey. According to Scheff ( '13), the first deciduous teeth of a rhesus monkey erupted on the thirtieth day and according to Lashley and Watson ('13), in another rhesus monkey, on the thirty-first day. Spiegel ( '29) reports that in a female Pithecus irus the first teeth appeared on the eighteenth day after birth and the last deciduous teeth on the 142nd day. Quite recently, Spiegel ('34) has published new data for the ages of eruption of the deciduous teeth in twelve to thirteen Java macaques and h d s that the first dentition erupts on an average between the ages of 1.9 and 23.4 weeks, but can individually be as late as 3.6 weeks at its beginning and as late as 40 weeks at its completion. According to the writer's ('33) data on ten to eighteen Pithecus rhesus, born in captivity, the eruption of the deciduous teeth occurs in this species on an average between the ages of 2.8 and 25.2 weeks, but varies individually to a very marked extent. It is very interesting to find that at least in one of the platyrrhines these teeth appear at a much earlier age than in any of the catarrhines for which we possess information. According to English ( '34), the i l appeared in a captive-born male night monkey (Aotus) on the second day and all deciduous teeth were present in the tenth week after birth. There exists little more information regarding the actually known age of eruption of the deciduous dentition of the higher primates besides man. For the gibbon we possess only two records: Robinson ('25) states that a Hylobates lar had only four incisors at the known age of 6 weeks, and the author ( '33) found in a Hylobates leucogenys that the upper middle and all four lower incisors have already erupted at the age ERUPTION AND DECAY OF TEETH IN PRIMATES 497 of 29 days. If both these observations are taken into consideration and compared with the author’s data on macaques, it can be tentatively stated that the first few deciduous teeth of the gibbon appear only slightly later than those of the macaque. According to the excellent report by Brandes (’28) on an orang-utan, born in captivity, the deciduous dentition of this ape began to appear in the fifth month and was complete a t the end of the first year of life. The author (’30) has already reported that in another orang-utan only the eight incisors and all the m l had erupted a t the known age of 1year. Two other orang-utans of known age have been examined by the writer at the Philadelphia Zoological Garden, a female aged 18 months and a male aged 204 months. In both the deciduous dentition was complete and no permanent teeth had appeared as yet. For the chimpanzee we possess one complete and two incomplete records on the eruption of the deciduous teeth in animals of known date of birth. According to Jacobsen, Jacobsen and Yoshioka (’32) the first milk teeth of the chimpanzee ‘Alpha’ appeared at the beginning of the third month and the last at the beginning of the seventeenth month. The chimpanzee ‘Julius ’ of the Philadelphia Zoological Garden possessed only five incisors at the age of 6;)months (Schultz, ’30)’ a t which age ‘Alpha’ had already fourteen of her deciduous teeth. I n the chimpanzee ‘Aprilla’ of the Philadelphia Zoological Garden‘ the first incisors (u. i l ) appeared at the age of 34 months and all eight incisors were present in the middle of the 6fth month. She was examined again at the age of 22 months, when her deciduous dentition was seen to be complete, and a t the age of 3 years and 8 months, it was observed that all her first Molars were fully erupted. For the gorilla there exist as yet no data on animals of actually known age, since none have ever been born in captivity. Brandes (’30)’ basing his conclusions partly upon the ‘‘Aprilla’ was examined by the author on two occasions; other data were obtained by a keeper and kindly sent to the writer by Dr. H. Fox. 498 ADOLPH H. SCHULTZ observations by Reichenow on the age intervals between the eruptions of the deciduous teeth in a captured gorilla infant, estimates that the first teeth appear in the third month and that all milk teeth are present at the age of 1year. Judging by these meager facts, the period of eruption of the deciduous dentition varies very considerably in all these primates, but appears, in general, to start and to be completed at earlier ages in the macaque and gibbon than in the three large apes. Even in the latter this period begins earlier and is much shorter than in man, in whom it extends approximately from the beginning of the seventh to the thirty-first month. Permanent dentition Our knowledge of the ages of eruption of the permanent teeth in primates of known age is unfortunately limited to the macaque, the chimpanzee (appearance of Ml),and man. I n addition, it has been possible to collect some observations on the age intervals between the eruptions of different permanent teeth in a few of the higher primates besides man. The data f o r the macaque are listed in table 2. Even these few cases show conclusively that the ages at which the various permanent teeth erupt can vary very considerably in different individuals. The sequence of eruption, however, is comparatively stable, with the exception of the Premolars which follow one another in particularly rapid succession. It is quite evident that the average ages, as given in the table, can be regarded as merely tentative values, but they are very much preferable to the previously published estimates. There exists apparently a long resting period before the eruption of the last permanent teeth, the M3. These teeth had not yet appeared in an animal nearly 6+ years old and not in three others more than 5 years old, but erupted in a fifth animal during its seventh and eighth year. It is quite possible, of course, that the last mentione’d ages may lie above the average age of eruption, or may be typical for males only. The author cannot agree, however, with the statement (as far as ‘erup- W (0 * 35 41 53 64 65 P I 35 25 34 27 33 34 36 27 36 I1 12 0 P1 P2 - UPPEU J A W M1 M2 .__ 40 i2 40 41 39 38 I2 m2 1112 46 56 P2 39 47 42 48 M2 1 ? 41 21 43 19 39 -__. 9 7 4s a1 2 8 21 20 20 23 M1 20 24 22 16 90 ? 1 ? ? ? 1 1 ? ? ? 90 M3 I1 I2 0 I1 35 35 27 36 41 38 33 38 I2 ml ml 45 49 P1 ml ml 49 61 61 13 5 I 12 5 60 44 -- 46 44 47 c c c 55 62 c c Pl - 11 5 49 - m2 m2 48 48 43 P2 59 m2 m2 48 P2 M1 M2 M3 38 46 41 51 M2 9 ? ? ? 79 1 90 7 49 15 - 79 1 ? 19 18 ? ? 19 ? 39 ? 42 20 40 1 19 --9 7 1 24 20 18 22 M1 -- -- - -- - LOWEU J A W mmlceys ( P i t h e m rhesue) of known age ? = tooth has not yet appeared at maximum age observed. ml ml 42 48 42 P1 ml ml 48 57 m2 m2 46 47 47 49 48 43 -5 5 5 47 68 48 9 14 10 c c c 55 65 c c - -- - -- 37 38 0 ~-37 pecimens 9 8 Average age (months) 33 s9 Sequence 1 3 6 ? ? 9 65' 72 97 76 73 B J H 42 47 65 76 106 6 6 6 6 6 G X - ___- 8EX NO. KAXIYUY AOE 3BSEEVED TABLE 2 The oge of eruption (in months) of the permanent teeth in them 500 ADOLPE H. SCHTJLTZ tion’ is concerned) by Marshall (’33) that “Normally at five years the eruption and calcification of the permanent teeth is completed, . . . .” and doubts that this conclusion is based upon observations on macaques of actually known, instead of merely estimated, ages. After this paper was written there appeared a report by Spiegel (’34) containing valuable data on the ages of eruption of the permanent teeth in three to eleven Java macaques (Pithecus irus). The approximate average ages of eruption for this material are as follows (changed from Spiegel’s lunar months into calendar months ; number of specimens in parentheses) : 1. M 1 = 19 months (ll), u. M 1 = 19 months (lo), u. and 1. 11= 31 months (8), 1. I 2 =34 months (8), u. I 2 = 38 months (6),u. and 1. M2 =43 months (6),u. and 1. P1 and P2 =52 months (5),u. and 1. C =53 months (4), 1. M3 =70 months (3), u. M3 =76 months (3). A comparison between these data and those in table 2 shows the close agreement between the corresponding results of Spiegel and those of the writer. All the major points regarding the sequence of eruption are identical and the average ages of eruption differ in most cases by only 1 or 2 months, though the individual values vary very considerably and both of the series are extremely small for the higher ages. Three males among Spiegel’s animals have reached an age at which the last permanent teeth are erupting, namely, 74, 76 and 78 months, respectively. Even the highest of these ages lies 1 year below the corresponding single record of the writer. This, however, is not surprising, in view of the general rule that the higher the average age of eruption of a tooth the greater are the individual variations of this age. According to the figures in table 2 as well as according to the data of Spiegel, the Canines of the males erupt considerably later than those of the females. The ages of eruption of the permanent teeth in chimpanzees are listed in table 3. In none of these animals are the dates of birth known. Their ages at the beginning of observation can be estimated with a fairly high degree of accuracy on g c1 TABLE 3 72 Pan I1 - i2 i2 73 74 70 72 66 67 r. r. 1. 71 6 70 70 69 71 C 74 74 90 89 M1 M1 M1 M1 78 83 36 36 36 36 36 36 33 33 91 91 76 80 78 76 84 84 m2 m2 m2 m2 ml ml ml ml 93 93 -871 871 C C C ml ml mS m2 P2 78 78 85 87 73 73 1 1 P I 1 1 M2 118 118 1 1 1 1 7 1 I ? 1 1 Y3 62 64 69 62 68 70 67 67 57 57 57 57 I1 90 92 95 95 99 1 95 1 C C C C C C - 0 -- 65 66 69 68 73 73 70 70 62 i2 60 60 I2 LOW= 89 89 76 78 m2 m2 m2 m2 m2 m2 JAW M1 M1 35 35 35 35 36 36 33 36 - 84 84 73 73 1 ? 1 ? 1 1 M2 104 - 104 126 126 1 1 1 1 1 7 1 1 M3 - - - - 68 74 M1 74 79 80 74 M1 - - 7s 81 s5 77 7 11 1 8 SO 81 79 80 71 71 57 61 ml ml P1 - - 4 90 8S 78 56 79 118 6S 67 94 116 13 9 12 2 10 16 3 5 14 15 -- 1 (without accompanying figure)= tooth has not yet appeared at maximum age observed. The data for the Arst four chimpanzees (except the ages of eruption of C in ‘Dwina’) have been calculated from the dates in the report by Bingham ( ’29). 66 66 66 r. 1. 133 nayton Average age (months) Sequence 68 68 r. 1. 126 1. i2 i2 61 58 1. C C r. 1. il il i2 i2 21 UPPEE J A W - - 0 I2 r. - - SIDE Evo 98 62 Wendy Dwina 60 MAXIMUM AQE. OBSERVED Billy NAYE The age of eruption ( i n months) of the permanent teeth in chimpanaees (Pan spec. ?) of estimated age, but known age intervals between eruption o/ different teeth - 502 ADOLPH H. SCHULTZ the basis of the following facts. Through the courtesy of Prof. Robert M. Yerkes the writer was informed that, according to the observations by Doctors Yoshioka, Jacobsen and Nissen of the Anthropoid Experiment Station of Yale University, the M1 appeared in three female chimpanzees with known date of birth between the ages of 32 and 35 months aud at 36 months all four M1 have erupted. According to the records of Bingham ( ’29), on four living chimpanzees (table 3), the eruption of the first I1 follows the appearance of all M1 in 21 months in two of the animals and in 31 months in the two others, i.e., on an average of 26 5 months. The dates of eruption of the M1 have been recorded by Bingham for all four of his chimpanzees. In the author’s estimation of the ages of these animals, as used in table 3, they are considered to have been 3 years old when all four M1 had appeared. The two Hopkins chimpanzees (‘Evo’ and ‘Dayton’) were obtained when they already had their M1. Their ages had to be estimated, therefore, as having equaled approximately 62 months (all M1= 36 months first I1 = 26months) at the date of eruption of the first 11. Bingham’s report was concluded when his oldest animal (‘Dwina’) had reached the estimated age of 80 months. Through the kindness of Prof. Robert M. Yerkes, the author received Dwina’s body after her death which occurred at the estimated age of 98 months. At the latter age Dwina had as yet no M3 and of her Canines the upper two were fully erupted, but the lower left was only partly out and the lower right had barely reached the alveolar margin. The ‘probable ages’ of eruption of Dwina’s Canines are given in table 3 accompanied by question marks. Judging by the fact that the upper M3 did not appear until 14 months after the lower M3 in Dayton, it may be assumed that the upper M3 of Evo will not erupt until at least 1 year after the appearance of her lower M3; i.e., not until she is approximately 138 months old. This estimate is, furthermore, + 503 ERUPTION AND DECAY OF TEETH I N PRIMATES supported by the finding that in another female chimpanzee2 which cannot have been less than 11+and not more than 123 years old, the lower M3 are not yet fully erupted and the upper M3 reach barely beyond the alveolar margin, though all other permanent teeth are fully out. The following justifiable estimates result in averages for the ages of eruption of the M3 in chimpanzees which are somewhat higher than the corresponding figures in table 3 : Cbimpanzss Dayton Evo P. A. L. 128 Average age of eruption 1. ius u. M8 104 months 126 months approx. 126 months 118 months approx. 138 months approx. 138 months 119 m o n t h 131 months Some further information regarding the ages of eruption of the teeth in chimpanzees became available during the final writing of this paper, when the author obtained the large bodies of a male and of a female chimpanzee (Hopkins collection, nos. 391 and 392, not included in table 18) which he had examined 6 years and 10 months before their death. At this first examination both animals had their complete deciduous dentitions, but as yet no M1. They were then, therefore, not over 3 years of age but, judging by their size and by the degree of attrition of their teeth, they were certainly over 2 years old. At the time of their death their ages must have amounted to not less than 9 and not more than 10 years. At this age both apes possess all their permanent teeth (the Canines in even the male fully erupted), except the M3, of which no trace can be seen in either jaw. It is of interest to mention in this connection that the duration of time between the first appearance of a tooth and its completed eruption differed very considerably in different 'The remains of this specimen (P. A. L. 128) were very generously given t o the author by Prof. J. F. F'alton, who had received the animal from Mr. E. Joseph, who states that he had obtained this chimpanzee originally 10) years before ita death and that upon arrival it had been about 18 m o n t h old. As experienced a man as Mi. Joseph would not likely have made a mistake i n his original estimate, amounting t o more than 6 months. This ape reached, therefore, a n age of 12 ( 26 months) years. 504 ADOLPH H. SCHULTZ teeth of the two Hopkins chimpanzees. I n general, t h i s duration was shortest in the Premolars, only slightly longer in the Incisors, and longest in the Canines. I n Evo the upper C took nine months and the lower C 7 months for their full eruption, whereas in Dayton these durations lasted approximately 3 months longer. Since it is one of the purposes of this study to compare t.he ages of eruption of the permanent teeth in man with the corresponding ages in other primates, it is necessary to obtain values for the ages of eruption in man which represent the approximately average conditions of different races and of the two sexes. Table 4 contains the data from the literature which have been utilized for the calculation of such generalized averages. The first seven rows are based upon table 13 by Suk ( '19), omitting the column for Filipino boys as too incomplete. The figures in table 4 are the arithmetic means of the minimum and maximum ages listed by Suk. The two question marks of Suk in his column for Czech boys have been arbitrarily replaced by 240 ( ?) and 228 ( ?), respectively, in order to introduce values for the ages of eruption of M3 in whites. The eighth row is inserted for the same reason; it represents a statement by Daffner ('02). The ninth row in table 4 gives the averages of the preceding rows. Next follow the averages of Rose's ('09, table 14) data. Since these are based upon very much more extensive series than the data of Bean and of Suk, and because they are real averages, rather than means of ranges of variations, they are treated as equivalent values to the averages in the ninth row. The last averages in table 4, therefore, are the arithmetic means of the preceding three rows only and are intended to show the approximate average ages of eruption in man in general. For quick, clear and complete comparisons between the data presented so far, the drawings in figure 1 are most suitable. The absolute ages of eruption in the three types of primates are compared in the left part of the figure. It is seen that the anthropoid ape is properly placed haif-way between the representative of the lower Old World primates and man. a P !4 F 4 8 g $ i F E Rase Riiae German Daffner 21,139 European 19,882Europern I Average of above 3 row8 S a m in years and monthu Elequence of eruption I Average of above Zulu ZllIU American American German-American German-American Czech Suk Suk andEluk Bean Bean Bean Matiegks Bean BACE TABLE 4 d 0 SEX 90 90 108 102 102 96 102 I2 .126 120 138 126 138 132 136 a 126 114 126 120 132 120 126 P1 7-5 4 89 10s 8-7 6 107 92 89 102 -- M1 M2 11-0 10 1st 77 6-5 2 10-3 7 us 139 11-7 12 153 149 13A 138 156 150 150 150 156 12-6 14 160 -- 79 78 66 78 78 66 78 78 78 125 136 121 -- 133 146 139 126 120 132 126 132 126 132 P2 ..... . . .. . . ... -..... -99 85 131 123 75 128 148 -- -- - -- 66 78 90 90 90 90 90 It -- -- - -- UPI'EB JAW 82 95 78 78 96 90 96 90 90 I2 134 126 114 138 120 138 126 126 135 126 114 132 120 138 126 132 P1 144 126 120 138 126 138 138 138 77 86 66 78 66 78 78 66 147 138 138 150 132 150 138 150 ... 216 216 2461 2281 ... ... ... ... .. .. ... ... ---........ 73 88 127 127 132 71 142 226 - - - - ---- 66 66 78 66 78 78 78 11 -- LOWEB JAW 9-11 16 dS9 91 18.9 1so 1S8 6-6 7-7 10-8 10-10 11-6 8 3 5 9 11 - 78 74 145 886 6-2 11-11 18-10 1 . 13 15 ... _-79 91 123 139 75 141 ... - 128 ---- ... 239 228 228 258 2401 ... ... ... ... M3 -- Approximate average ages (in monthe) of the eruption of the permanent teeth in man 506 ADOLPH H. SCHULTZ The beginning of the eruption of the permanent dentition occurs in the macaque at the age of 1+ years, in the chimpanzee a t twice this age, i.e., at the end of the third year, and in man at twice the latter age, namely, at 6 years. The completion of the permanent dentition, however, is accomplished in the chimpanzee at an age which is relatively nearer to the 400 U. M U.M UM i Fig.1 Diagrammatic representation of the absolute and the relative ages of eruption of the teeth in macaque, chimpanzee and man, based upon the averages in tables 2, 3 and 4. corresponding age in the macaque than to that in man. It is of particular interest to note that not only in man, but also in the two other primates exists a very considerable resting period before the eruption of the M3. A similar resting phase occurs after the eruption of the M1 in the macaque and the chimpanzee, but not in man. These periods of rest ERUPTION AND DECAY OF TEETH IN PRIMATES 507 during the process of eruption of the permanent dentition are even more clearly apparent in the drawing on the right of figure 1. In this drawing the age of eruption of the last permanent teeth (u. M3) is assumed to represent what may be termed ‘dental maturity’ and is shown to equal 100 on the scale which starts with birth equal 0. On this scale of relative ages the periods for the eruption of the deciduous dentition differ comparatively little in man and chimpanzee. The resting periods between the completion of the deciduous and the commencement of the permanent dentitions are approximately the same in all three types of primates, amounting to roughly 15 per cent of the ages between birth and dental maturity. The Incisors appear at very similar relative ages in man and in the macaque, but in the former they follow immediately after the M1, which erupt comparatively late, whereas in the latter there exists a striking period of inactivity between the eruptions of M1 and of Incisors. The last mentioned resting phase is even more pronounced in the chimpanzee than in the macaque and, as will be shown later, seems to be characteristic of all Old World primates, except man. That this intermission in the process of eruption of the first few permanent teeth exists also in the gorilla can be definitely stated on the basis of the following observations which indicate in addition the duration of time between the completion of the deciduous dentition and the first appearance of permanent teeth: The male lowland gorilla ‘Bamboo’ of the Philadelphia Zoological Garden possessed only his incisors and m l in August, 1927; Four months later, when weighing 17+ pounds, his deciduous dentition was completed. In November, 1929, Bamboo had as yet no permanent teeth, but all his M1 were seen to be fully out in June, 1930, and had most likely started to appear in January of that year, or 25 months after the deciduous dentition was complete. Only the upper and the lower I1 had been added to Bamboo’s dentition in the middle of December, 1931, i.e., not until 23 months after the beginning eruption of his M1. The male lowland gorilla ‘N’gi’ of the National Zoological Park had 508 ADOLPH H. SCHULTZ gained his complete milk dentition early in 1928 (probably in February). His M1 were found to have erupted (the lower ones completely, the upper ones partly) in March, 1930, or, as in Bamboo, 25 months after the completion of his milk dentition. At the death of N’gi, in March, 1932, only the I1 of both jaws had been added to the permanent dentition, i.e., the resting period between the eruption of M1 and of I1 was 24 months, or practically the same as in the other gorilla, and strikingly like this period in chimpanzees. That there exists a resting stage between the eruption of the M1 and that of the Incisors in Old World monkeys and apes was recognized by Krogman ( ’30), who had examined fairly extensive series of juvenile skulls of these primates and has clearly indicated this resting stage in his table on the sequence and rate of eruption of the teeth. This same table, however, does not show the long resting period preceding the eruption of the M3 in the macaque and the chimpanzee. I n man there is found a definite resting period between the eruption of the Incisors and that of the subsequent permanent teeth, a period which has no equivalent in chimpanzees and in macaques. I n the latter two the M2 appear comparatively early and the C relatively late, whereas in man the reversed conditions form the rule. This is discussed more f d y in the chapter on the sequence of eruption. In this chapter it remains t o refer briefly to two recent publications which contain statements in regard to the age of eruption of the teeth in apes. Zuckerman (’28), after repeated examinations on some chimpanzees of estimated ages, concludes, that: “The available data indicate that the durations of the chimpanzee tooth stages are practically the same as in Man. The first permanent molar erupts between five and six years, and the last molar at fifteen, or later.” I t is evident from the data presented in this paper that the writer cannot agree with the statement of Zuckerman which must have resulted from erroneous age estimates and perhaps have been influenced also by abnormally retarded eruptions of certain teeth in one or more of his few captive animals. ERUPTION AND DECAY OF TEETH IN PRIMATES 509 Without giving his evidence, Sir Arthur Keith ('31) has published a diagram showing the periods of eruption of the teeth in anthropoid apes. I n this figure it appears that the permanent teeth of, e.g., the chimpanzee start to erupt in the middle of the fifth year and have completely erupted not until the end of the fourteenth year. These and many other incorrect details justify the assumption that this comprehensive, but, unfortunately, premature diagram is based largely upon estimates, rather than on observations on animals of known age. SEQUENCE O F ERUPTION O F PERMANENT TEETH The following data appertaining to the sequence of eruption of the permanent teeth are based upon the study of dead specimens of differing ages. For this study records were made not only of each individual dental formula, but also of the teeth which had not yet fully erupted a t the time of death of the animal. I n each instance of incomplete eruption of a tooth the degree of eruption was recorded as being approximately one-fourth, one-half or three-fourths complete. Though these degrees had to be omitted in the final tables, they have been given thorough consideration in arranging the probable normal sequence of the different dental formulae and in constructing the generalizing diagram in figure 2. If, e.g., the upper M1 are only one-fourth erupted, whereas the lower M 1 are three-fourths out, it is fully justifiable to assume that the lower M1 had appeared before the upper ones. The frequency distribution of the different dental formulae within a large series of juvenile specimens permits conclusions in regard to the rapidity with which certain teeth follow each other. For instance, among 315 young macaques (table 15) there are only 5 in which merely the upper P1 of the Premolars are present, and only 5 other specimens in which also the upper P2 and lower P2 have erupted. This is a reliable indication that the eruption of these Premolars takes place in rapid succession, namely, at the ages of 47, 48 and 49 months, as shown by table 2. On the other hand, since there 510 ADOLPH H. SCHULTZ are (in table 15) 69 macaques in which only all M1 have appeared, it is safe to conclude that there must occur a very marked resting period before the dental formula becomes changed by the addition of further permanent teeth. The correctness of this assumption can be verified by the data in table 2, according to which this particular resting period averages in macaques 11 months. The tables of the dental formulae of dead material contain a column for ‘exceptions’; i.e., unusual cases found only in single specimens, which most likely do not represent the average sequence of eruption. The relative frequency of exceptions indicates the degree of variability of the sequence of eruption in a particular primate genus, and any restriction of all or most exceptions to certain ages tends to show which phases of tooth eruption are most likely to proceed in irregular fashion. Before discussing the findings regarding the sequence of eruption of the permanent teeth in primates it would have been desirable briefly to review this sequence in other mammalian groups, in order to be able to decide afterward whether the particular modes of eruption in primates represent a general mammalian feature or are characteristic for only the order of primates, or even only the suborder Simiae. Unfortunately, information on this subject is extremely scanty and the author can merely contribute new data on one mammal besides the primates. These data are collected in table 5 and are the result of the writer’s examination of the dentitions of twenty-six freshly killed dogs, in none of which all of the permanent teeth had completely erupted. Based upon this table the sequence of eruption of the permanent teeth of the dog can very tentatively be given as follows: u. P1; 1. P1; u. and 1. 11; 1. 12; u. 12; n. and 1. 13; 1. M1;u. M1; u. P4; 1. M2; 1. C; u. P 2 ; 1. P 2 ; u. C ; u. P3; u. M2; 1. P4;1. P 3 ; and 1. M3. As will be shown later, this sequence of eruption in a carnivore differs very significantly from the sequence in any of the primates studied. In contrast to the latter, in the dog the P1 are the first permanent teeth to appear and these 511 ERUPTION AND DECAY OF TEETH I N PRIMATES are followed by the Incisors and not until afterward are the M1 added to the dentition. According to the table given by Ellenberger and Baum ('15), the first and second Molars erupt before any other permanent teeth in domesticated ungulates. These Molars TABLE 5 Dental formuhe of twentysix dogs with at least purt o f the permanent deatition, arranged to show the sequence of eruption of the teeth (for abbreviations see chapter on Ezplanativns) NUYBLB Or SPECIMENS 1 I DENTAL Tommu i i i c P1 m l m2 m3 iiic mlm2m3 INCOYPLliTliLY EEUPTID u. P1 2 i i i e P 1 m l m2 m3 i i i c PI m l m2 m3 n. and 1. P1 1 I i i c P 1 m l m2 m3 I i i c P1 m l m2 m3 u. and 1. P1 and I1 1 I I i c P1 m l m2 m3 I I e P1 m l m2 m3 u. I2 and 1. P1 I I i e P1 PB m2 m3 IIicPl ..dm3 1 I I l c P1 m l m2 m3 I I1 c P l m l m2 m3 M1 u. and 1.13; 1. M1 1I I c P l m l m2 m3 M1 i i I e P1 m l m2 m3 M1 2 I I I c P1 m l m2 P 4 M1 I I I c P 1 m l m2 m3 M1 M2 u.and1.13; u.P4 11 I I e P1 m l m2 P 4 351 1. M2 I I I C p1 m l m2 m3 M1 1 I I I e P1 m l m2 P 4 M1 I I I C P l m l m2 m3 M1 M2 u. P1; 1. C; 1. M2 1 I I I c P1 P 2 m2 P 4 M1 I I1 C P1 P 2 m2 m3 M1 M2 u . m d l . P 2 ; 1.c; 1. M2 1 I1 I C P 1 P2 P 3 P4 M1 M2 I I I C P 1 m l m2 m3 M1 M2 1 I I I C P l P 2 P 3 P 4 M1 M2 / I I I C PI m l P 3 P 4 M1 M2 u.andl.P3; u.M2 I 1. M3 (in all eases) 10 - I I I C P 1 P 2 P 3 P 4 M1 M2 11I C P l P 2 P 3 P 4 M1 M2 M 1. M2; u. P 2 and P3 .. I I I C m l P 3 P 4 MI. MO I I I C P 1 P3P4MlM2 I 1 .. 512 ADOLPH E. SCHULTZ are followed in cattle, e.g., by the I1 and 12, then by the P1 and P2, then by the M3 and P3, and finally by the I3 and 14. That this order of eruption differs also from the typical sequence of the appearance of teeth in primates will be evident from the discussion to follow. NEW WORLD MONKEYS The entire material of primate skulls which the author was able to study contains only three specimens of marmosets (Oedipomidas) in which not all of the permanent teeth had fully erupted. It is impossible, therefore, to give more than very fragmentary information regarding the sequence of eruption in these primates, which are the only available representatives of the family Callithrichidae. The youngest of these three specimens shows the following dental formula: IIcmmmMM I I c P m m M Y the lower P1 being only partly erupted. I n the two older specimens all the permanent teeth are present, but the upper C are only one-fourth out. As a tentative conclusion, it may be stated that in Oedipomidas all M2 appear before any of the Premolars and that the Canines are the last teeth to erupt completely. I n the platyrrhine genus Saimiri (table 6) the M2 erupt before any of the Incisors have appeared and the lower M3 erupt before any of the Premolars, though these statements are based upon only single specimens and have to remain very tentative until codrmed by observations on additional material. As will be shown, these particular conditions represent exceptions among New World monkeys, but repeat what forms the rule in langurs. The most probable, normal sequence of eruption of the teeth of squirrel monkeys is shown in figure 2. As in all other genera of the platyrrhine family Cebidae, the Canines of Saimiri are considerably larger in males than in females. Judging by the details regarding incompletely erupted teeth (table 6), this secondary sex difference is not correlated with any clear sex difference in the relative age or sequence of eruption of the Canines. EBUPTION AMD DECAY OF TEETH IN PIUMATES 513 The platyrrhine genus Alouatta (table 7) shows some minor peculiarities in the sequence of eruption of its permanent teeth. As summarized in figure 2, the lower I1 are followed not by the upper 11, as would be expected, but by the lower 12. The upper I2 do not appear until the lower M2 have erupted. In both sexes the upper C complete their eruption after that TABLE 0 Dental formulae of twenty-three a p i w e l monkeys (Saimiri) with at least part of the permanent dentition, arranged to shoru the sequence of eruption of the teeth I INCOMPLETELY LBUPTED I iicmmm i i c m m m ~ L MI iiemmmM iicmmmM u. M1 IiemmmMM iicmmmMM u. I1 IIemmmMM LIcmmmMM u. I2 IIcmmmM M IIemmmMMM L M3 3dand3Q IIePPPMM IIePPPMMM In 4 caee8 u. P1 and in 2 of these 1. P1 ldand2Q IICPPPMM IICPPPMMM In 3 caeea u. and L C 5dand39 IICPPPMMY IICPPPMMY In 1 Q u. M3; in other 2 Q and in 5 6 u. C; in 2 Q and 3 d 1 IcPPPMMM d w. IePPPMMM (alwaye 1. C farther out) 1. c of the lower M3. I t is noteworthy that the three ‘exceptions’ are wild specimens and represent only minor variations, occurring during stages of growth characterized by rapid changes in the dentition. The capuchins represent probably the least specialized genus of the platyrrhine subfamily Cebinae. Their sequence of eruption is practically identical with that occurring in most AYEOICAN JOUBNAL OW PHYSICAL ANTHBOP0U)QY. VOL. XIX, XO. 4 514 ADOLPH H. SCHULTZ -M4-Mc 11 GORILLA - Mi Ii -7- 12 cn I2 M4 12 Ii 11 M 2 M2 m Pr Pf C M2 I2 M2 P2 rt C Ms M3 Ft M4 b I2 MiC Mi PAN -: M4 M3 M4 PON60 - M~ M4 HYLOBATES M4 Ii 14 14 I2 I2 I2 14 Mi P4 M3 C M3 C M3 P2 M2 I2 M3 c P2Yi M2 M2 Ii I2 C Mt-2 M2 PITHECUS 4 Mi 2 4 3 14 I2 M2 PC P2 C M3 MC PAPIO - M, 14 I2 M2 P4 R C M3 M4 I4 I2 M2 R R c M3 LASIOPYGA 2 4 M - T M4 14 12 C Ma CoLo6us - M~ h M2I2 P4 P2 Ms NASALIS - Mi I4 -ii-i% In5 ItM2 CZR P2 M2 Ir 12 M3 MI C Ii Mi M Mj S Pz Pi c PYGATHRIX h M, Ma 2 4 MC ATELES- M~ M4 CEBUS --H4 -M2R R P3 CM3 f i R P3 C M3 M2 P4 Pz P3 c M 3 M2 P4 P2 P3 .c M3 12 M2 Pi P2 P3 cM3 14 12 fi I412 I4 I2 14 I2 M4 ALOUATTA M~ ~ M4 SAIMIRI - M~ I1 4 I2 4 M2 14-2 M2 14 I2 fi 2 3 m p I P2 P3 PI . 3 cM3 SEQUENCE OF ERUPTION Fig.2 Diagrammatic survey of the sequence of eruption of the permanent teeth in m e r e n t genera of primates, based upon tables 4 and 6 to 19. Resting periods are indicated by blank spaces between the symbols for successive teeth. The thin horizontal lines above some of the letters indicate that the particular upper and lower teeth underneath the line ean vary markedly i n their sequence of eruption and this, usually, in connection with a rapid succession of eruption. ERUPTION AND DECAY OF TEETH I N PRIMATES 515 TABLE 7 Dental formulae of seventy-k howlers (Abuatta) with at l m t part of the permonen: dentition, arranged to show the sequence of w p t w n of the permanent teeth ~ NUKE= OI BPICIYENB INCOYPLITELY EBUPFEI) 'INTu mBYULA I I 6 iiemmm iiemmmM 3 iiemmmM iicmmmM In 3 cases u. M l 6 iicmmmM IiemmmM In 2 easea L I1 2 iiemmmM IIemmmM In 2 eaaea 1. I 2 3 /I I I c m in m M M em IIem mm M IIemmmMM 5 In 5 eaaea 1. M 1 111 3 eases 1. M2; in 2 cases u. I1 IIcmm mM M IIemmmMM 7 IIemmmMM II ePm m MM In 7 esaes1.Pl; in 2 eaaeau. M2 5 IIePmmMM IIcPm mMM In 5 eases n. and 1. P1 1' I I II e P P P M M In 4 cases u. M2 and in 1of thes u.12 In 1 case u. P 2 and 1. P 3 2 IIePPmMM In 2 eases 1. Cand u. and 1. P 2 ; I I C P P m M M M in 1 ca8e 1. M3 2 I I C P P P M M In 2 eaaeau. Cand L M3; in 1 I I C P P m M M M caael. C 12 [icmmmhI W. LicmmmMM In 3 eases u. 12 and in 2 of these 1.M2 7 2 LXCIRTIONII (BINOLE OAeES) I I I C P P P M M In 11 cases u. C; in4 cases L C; I I C P P P M M M in 2 eases 1. P 3 I I C P P P M M M I n 10 eaaeou. C; i n 5 easea u. 6gand5p I I C P P P M M M M3:inleaaoI.P3 CI c P P PMM C I e P m m M M"' CIePmPMM 1I C P P P M MW. 516 ADOLPH H. SCHULTZ the catarrhine genera. According to table 8 and as shown in figure 2, the sequence of eruption of the teeth in Cebus is: M l , I l , 12, M2, P1, P2, P3, C and N3. The order of appearTABLE 8 Dental formulae of flfty-one cupuchins (Cebus) with at leqst part of the permanent dentition, arranged to show the sequence of eruption of the permanent teeth gsfi:: DENTAL FORMULA I INCOMPLETELY EgUPTED iiemmm iicmmmM In 2 cases 1. M1 IiemmmM IiemmmM u. and 1. I1 l2 II emmmM IIcmmmM kn 5 emes u. I 2 and in 1 of these u. M1 lo IIemmmMM IIemmmMM In 3 c88es u. M2 IIemmmMM IIcmmPMM II e P P m M M IIcPmmMM IIemmmMM ldanal?I I C P m m M M 2d I IePYP M M IIcPPPMM 2p IICPPPMM IICPPPMM ’ EXCEPTIONS (SINQLX OASES) I /I P3 u. P 2 In 2 cases 1. C and 1. P1 J.n lcaseu. 1. P1 a r c [ I e P P P M M ps In 2 cases P.and 1. C [IemmmMMM [ICPmmMM mmM M M [ 1 C.P IICPPPM M In 4 easee 1. M.7 nnd in 2 d i I C a p P M M M of ,these u. C CIcmPPMM [ICPPPXMM I I C P P P M M M In 7 cases u. M3;in 3 d CIemPmMJdM [IemmPMMM dand 0 11 I c P. P P M M M cases u. C W. ance of the Premolars can vary a good deal, the different teeth most likely ernpting in rapid succession. All ‘exceptions’ belong to the phase of dental development after the eruption of all M2. Only one of the four exceptions is a ERUPTION AND DECAY OF TEETH I N PRIMATES 517 captive specimen, and this is a normal animal in every respect, except that some of the deciduous molars have b.een retained abnormally long-a condition which has caused also the three exceptions in wild capuchins. Judging by the cases in table 8, TABLE 9 Dental formulae of forty-two epider monkeys (Atelee) with at least part of the permanent dentition, arranged to l o % the sequence of emption of the pewnanent teeth ~~~~E~~ DENTAL MBYULA INCOYPLETELY EPUPI%D iiemmm iiemmmM In 3 cases 1. M1 iicmmmM iiemmmM I n 2 caaea u. and 1. M1 iiemmmM IIemmmM 1. I1 and I3 IIemmmM I I e m m m ~ In 1cage u. and 1. I 2 IIcmmmM IIcmmmMM In 2 eases 1. M2 IIePmmMM IIcPmmMM u. and 1. P1 and u. M2 2dand4p IIePPPMM IIePPPMM In2caeeal.P2andP3;in 1casel.PT 2 dana 6 p IIcPPPMM IICPPPMM [n 8 eases 1. 3 2d 1d a n d 5 0 3dandlO C EXOEPTION9 (9INOLE O U M ) IIePPPMM IIemmPMM w. IIePPPMM - w. IIePPPMMM g IIePPPMM In 2 case9 1. C and M3 IICPPPMMM IICPPPMM In 1 d a n d 19 u. C a n d L M IICPPPMMM IICPPPMMM it seems highly probable that the Canines start and complete their eruption slightly later in males than in females. I n the last and most highly developed genus of New World monkeys, Ateles (table 9 ) , the order of appearance of the 518 ADOLPH H. SCHULTZ permanent teeth is practically the same as in Cebus. In the former the upper C seem to erupt after the lower M3 and, therefore, relatively late. The available material of Ateles does,not permit a safe conclusion in regard to a possible sex difference in the relative ages of eruption of the Canines, such as has been demonstrated for Cebus. Again it is found that the ‘exceptions’ are wild specimens, so that it can be stated that among platyrrhines irregularities in the sequence of eruption are not in any sense caused by conditions of captivity, such as faulty diet or disease. That these exceptions do not represent by chanceqecies differences is proved by the fact that the great majority of the specimens in table 9, including the exceptions, are of the species Ateles geoffroyi. In none of the primate genera studied has it been possible to demonstrate species differences in the sequence of eruption. It is conceivable, however, that a great deal of suitable additional material might reveal slightly different rules for the order of appearance of some of the teeth in different species of the same genus. As far as the writer can ascertain, No11 (1866), Huxley (1871) and Bolk ( ’26) are the only authors who have made some previous statements ‘in regard to the sequence of eruption of the permanent teeth in platyrrhines. Noll, based upon observations on the juvenile skulls of only one Cebus and one Lagothrix, concludes correctly that in platyrrhines the M1 appear first, t o be followed by the Incisors and immediately thereafter by the M2. Huxley merely mentions that in Alouatta (=‘Mycetes’) and in Ateles the Canines usually make their appearance before the M3, a statement which agrees with the corresponding findings of the writer. Without recording the number of specimens examined, Bolk claims that in Saimiri (=‘Chrysothrix’) and Cebus the teeth of the lower jaw erupt in the following sequence: 11, 12, M1, M2, P1, P2, P3, (all P simultaneously), C, M3, and adds that in Ateles the Premolars erupt at the same time as the M2. Bolk repeats clearly that, in contrast to catarrhines, in the platyrrhines the M1 do not appear until after all Incisors have ERUPTION AND DECAY OF TEETH IN PRIMATES 519 erupted. How Bolk could have arrived at this particular conclusion is a mystery, since it is not supported by a single specimen among the 195 young platyrrhines examined by the writer. Bolk’s claim is specially puzzling in regard to Saimiri, because in this genus the Incisors do not appear until after the eruption of even the M2. It may be mentioned in this connection that this (quite evidently erroneous) h d i n g of Incisors being followed by M l in platyrrhines, whereas by &I2 in catarrhines, is regarded by Bolk as a remarkable support for his well-known hypothesis, according to which the M1 of catarrhines are supposedly homologous to the m3 of platyrrhines. OLD WORLD MONKEYS The Asiatic genus Pygathrix shows an extreme departure from the general rule regarding the sequence of eruption of the permanent teeth in primates. As is evident from table 10, in the langurs all M2 erupt before any of the Incisors and all &I3 before any of the Premolars and Canines. There are some isolated exceptions to this generalization, but two of these occur in captive specimens and in the single wild specimen, not conforming to this rule, only the upper M3 are unusually late in appearance. On the basis of the data in table 10, it seems probable that, in general, the Canines of males erupt slightly later (or more slowly) than those of females. Bolk (’26) states that he had at his disposal a series of successive stages representing the sequence of eruption of the teeth in a langur and pictures eight specimens with incomplete permanent dentition. According to this material the teeth of Pygathrix aurata (=‘ Semnopithecus maurus’) erupt in the following order: M1,11, 12, M2, P2, P1, C, M3. Again, this finding of Bolk does not agree with the corresponding result of the writer (fig. 2 and table 10). This discrepancy might possibly be due to some species difference, though the writer’s series of sixty-three young Pygathrix contains many different species (but no P. aurata!) without showing different se- 520 ADOLPH H. SCHULTZ quences of eruption ;or it might be explained in part by assuming that Bolk speaks only of the completed, rather than started, eruption of the teeth. That Bolk generalizes without giving consideration to the degrees of eruption is evident, TABLE 10 Dental formzllae or eizty-three langura (Pygathriz) with at least part of the permanent dentilion, arranged to show the sequence of eruption of the permanent teeth ~ DENTAL ~ mBMULA ~ E l4 1' iicmmM EXCEPTIONS ( S I N O W CASES) INCOYPLLTELY L ~ EPUPTID ~ /In 2 easeY n. M1 iiemmMM iiemmMM I n 2 cases u. M2 3 I IiemmMM In 2 easesn. 11 IiemmM e. IicmmM 3 IiemmMM IlemmMM [112~aWs1.12;in1~ase(e.) u.M2 IiemmM IIemm MM a I Iem mM IIemmMM In 3 eases u. 12 2 I Iem In 2 eases u. I 2 and 1. M3 IIemmMMM 3 IIemmMMM IIemmMM W. II In 2 cases u. M3 lIemmMMM '* [I-mmMMM 1. C and P1 LICPPMMM I1' I I I C P P MMM I p p M3f ~n 3 easeel. C; in 1 ease u. ~3 1 I e P P lv, hi M w * d IICPPYMM cp [ICmPMMM Iu. and 1. C andn. PI I I C P P M M M I n 4 and 4 Pu. M3;in 13 6 and 3 9 u. C; in 3 3 1. C IIC PPM MM IICPPMM I I C P PMMM I e.g., from the fact that in the text he claims that all I2 erupt before the M2, but in his corresponding drawing (pl. .I,fig. 7) the upper I2 are barely visible, whereas the upper and lower M2 have nearly one-half erupted. ERUPTION AND DECAY OF TEETH IN PRIMATES 521 For the second genus, Nasalis, of the subfamily Colobinae, there are not enough young specimens available to study the sequence of ‘eruption in more than an incomplete and tentative manner. According to table 11 and the records on the degrees of eruption, the lower M2 appear simultaneously with the upper I 2 and the upper M2 follow immediately after the latter. Again it is found that the Canines of males seem to erupt somewhat later than those of females. TABLE 11 Dental formulae of seven proboscis monkeys (Nosulk) with at lea& part of the permanent dentition, arranged to show the sequence of eruption of the permanent teeth. There are no ‘exceptions’ NUMBBE O F SPPCIYINS 1 1 19 2Jand19 i 1 DENTAL FOEMULA I IXWOOMPLETLLY EBW-D IIemmM I I c m m If c. I 2 IIemmMM IIcmmMM 11. and 1. I2 and u. M2 IIemmMM IICmmMM IIePPMM IICPPMM I rCPPMMM IICPPMMM ITnl O u . * n d I . M 3 ; i n ~ d u . a n d l . C I n the genus Colobus (table 12) the M2 erupt immediately before the I 2 of the corresponding jaw. This is of special interest, because it permits the generalization that at least the three genera Colobus, Nasalis and Pygathrix of the subfamily Colobinae have in common the tendency to have their M2 erupt unusually early. This tendency is least pronounced in Nasalis, in which the M2 follow immediately after the 12; it is quite evident in Colobus, in which the M2 appear before the 12; and it is most pronounced in Pygathrix, in which the M2 precede even the I1 (fig. 2). The same tendency exists also in Saimiri among the platyrrhines. 522 ADOLPH H. SCHULTZ Selenka (1899), based upon his examination of only four guereza skulls, has claimed the following order for the eruption of the teeth in Colobns: u. M1,l. M1, u. 11,l.11,u. 12,l. 12, u. M2, 1. M2, u. C, 1. C.,u. P1,l. P1, u. P2, 1. P2, u. M3, 1. M3. TABLE 12 Dental fornwlae of Pfteen guereaas (Colobus) with at least part of the permnent dentition, arranged to 8how the 8eqvence of eruption of the permanent teeth. There are no ‘ezceptions’ DENTAL M B Y U l d INCOYPLLTELY LPUPTED 1 iicmm iiemmM 4 iiemmM iicmmM 1 IicmmM IIcmmM I2 1 IicmmMM IicmmMM .M2 1 IicmmMM lIcmmMM 12 and u. MZ 1 IIcmmMM IIcmmMM .I2 2 5 IIcPPYM IICPPMMM n 2 cases 1. C and 1. M3 Id IICPmMMM IICPPMMM P2 3d IICPPMMM IICPPMMM n 3 cases u. and 1. C (1. C more out than u. C) M1 n 1 case u. M1 I n comparison with figure 2, it is readily seen that Selenka’s data do not agree with the writer’s findings. There can be no doubt, e.g., that Selenka is mistaken in his claim that all the upper teeth erupt before the corresponding lower ones, and it is d a c u l t to understand how such a definite conclusion can possibly be reached from a study of only four specimens. ERUPTION AND DECAY OF TEETH I N PRIMATES 523 The following three genera, representing the subfamily Lasiopyginae, show practically identical sequences of eruption of their permanent teeth. This particular type of sequence is also found in the gibbons and the three large apes and, with only insignificant alterations, in the platprrhine capuchins and spider monkeys. I n all these primates the M1, as the first permanent teeth, are followed by the 11, then by the 12; after the Incisors appear the M2, to be followed in varying order by the Premolars, afterward by the Canines, and finally by the M3. The lower teeth erupt with few exceptions before the corresponding upper teeth. These rules are clearly illustrated by the successive dental formulae of Lasiopyga (table 13). That there occurs a considerable resting period between the eruption of the M1 and the I1 is indicated by the fact that there are eighteen guenons with only all M1 out, whereas only two specimens showing the additional eruption of the 11. I n a similar way it may be concluded that in Lasiopyga, as in Pithecus (fig. l), there occurs a second marked resting period before the eruption of the lower M3 since all permanent teeth, except the M3, were found in twenty-six guenons, the highest number of specimens with one and. the same dental formula. A studymf .the data in table 13 reveals the fact that the Canines of males erupt relatively later than those of females. As mentioned above, Papio (table 14) shows practically the same sequence of eruption of its teeth as does Lasiopyga. There may exist a slight difference in the order of appearance of the Premolars, but in view of the marked variability in this particular sequence, which takes place in rapid succession, such a difference is still far from being definitely established. Again it can be stated that the Canines of the males make their appearance slightly later than those of the females, at least according to the data in table 14. The material in this table contains thirty-four captive specimens, yet there are only two ‘exceptions,’ only one of which being a captive speaimen and both representing only slight departures from the usual sequence of eruption. 524 ADOLPH R. SCHULTZ TABLE 13 Dental formdue of 100 guenone (Losiopyga) with at leaat part of the permanent dentition, arranged to show the sequence of eruption of the permanent teeth NUYBEB OP SPECIMENS -- INCOYPmTtLY tPVPT6D EXCEPTIONS (SINOLE OASES) 4 iicmm iicmmM I n 4 cases 1. M1 18 iicmmM iicmmM In 3 cases u. M1 1 IiemmM iiemmM u. I1 1 IicmlnM IicmmM u. I1 1 IicmmM IIcmmM 1. I2 5 IIemmM IIcmmMM I n 5 cases 1. M2; in 3 cases 11. I 2 6 IIcmmMM IIcmmMM I n 4 cases u. M2 2 tIcPmMM IIcmmMM In 2 cases u. P1; in 1case u. M2 2 IIePPMM CIcmPMM In 2 cases u. P1, u. P2 and 1. P 2 IIcPPMM IIcPmMM 2d IIcP P MM IIcPPMM In 1case 1. P1 IIcmmMM I ICPm M M " iicmmM IIcmmM W. '- 5dandlO IIcPPMM IICPPMM I n 6 cases 1. C ; in 3 eases 9 dand 1 7 p IICPPMM IICPPMM I n 9 6 and 119 u. C; in 9 8 1.C; in 2 91. P1 5dsnd79 IICPPMM IICPPMMM In4du.C;inl~l.Pl;in IICmmMM 10 cases 1. M3 I I C P P M M MW'? 8dandlP IICPPMMM IICPPMMM In8du.C; in4Sand1? 1. P1 u. M3 IICPPMMM I I C P P M M . w.? 525 ERUPTION AND DECAY OF TEETH I N PRIMATES TABLE 14 Dental formulae of #fty-five baboons (Papio) with at least part of the permanent dentition, awanged t o show the sequence of eruption of the permanent teeth INCOYPLETBLY EEUPTID 4 iiemm iicmmM In 4 c u e s 1. M1 13 iicmmM iicmmM tn 4 eases u. M1 1 iicmmM IicmmM 1. I1 3 IiemmM IicmmM In 1 case u. 11; in 1ease 1. I1 5 IicmmM LIcmmM In 4 cases 1. I2 and 2 of these eases u. I1 1 IIcmmM 1 1 c m m b1 11. 3 IIemmM IIcmmMM I n 3 eases 1. M2 ; in 1 case u. I2 3 IIemmMM IIcmmMM In 1ease n. and 1. M2 19 IIcmmMM IICPmMM u. M2; 1. C; 1. P1 19 IIcPmMM IICPPMM u. P1;1. C; 1. F1 IIcPPMM IICPPMM I n 1 S 1. C a n d l . PI ldandl? 3 d and 6 9 IIICPPM '1 3d M 111C P P M M I IXCIPTIONS (SINOLE OASES) icmmM :IemmM C I% I n 3 d a n d 1 9 u . a n d l . C ; in 19u.Y2 IICPPMM ICPP MM Y I n 3 9 1. M3; i n ' l 8 u. and, 1. C IICPPMMM IICPPMMF T% 3'cases u. M3 : in 1 case u. C LICPmMM L I C P m M M m"o 526 ADOLPH H. SCHULTZ Huxley (1871)has stated that in baboons (=‘Cynomorpha’) “the permanent canines make their appearance before, or, at least, contemporaneously with, the hindermost molar in both jaws.” The formula of Krogman (’30)for the sequence of eruption of the permanent teeth in baboons agrees, in general, very closely with the corresponding findings of the writer, though Krogman did not recognize that, besides the Incisors, also the Canines and Molars erupt in the lower jaw slightly before the same teeth appear in the upper jaw. For this study it was possible to examine a series of 315 skulls of young macaques3 (table 15), besides the living macaques (table 2), so that the sequence of eruption of the permanent teeth can be established more definitely for Pithecus than for any other genus of primates, besides man. There can be no doubt that the first permanent teeth to appear in macaques are the lower M1. They erupted before the upper M1 in all the living specimens studied (the differences between the ages of eruption of the lower M 1 and the upper M1 varying between 1 week and 2 months), and in 31 (17 14) of the skulls in table 15. No skulls were encountered showing indications of the upper M 1 having appeared before the lower M1. The second group of teeth to be added to the permanent dentition are the medial Incisors. The lower I1 appeared before the upper ones in 3 living animals (table 2) and in 7 of the skulls (table 15, considering also differing degrees of eruption). The reversed relation existed in 4 living specimens and in 13 skulls. The upper and lower I1 erupted simultaneously in 2 living macaques and most likely in at least 16 of the skulls. The last condition may be accepted as the general average for Pithecus and is shown in this way in figure 2. Of the lateral Incisors the lower ones precede the upper ones in the vast majority of the cases (in 41 of the skulls, considering again the differing degrees of eruption). In living macaques the lower I 2 erupt + ‘The dental formulae of 200 of these young macaque skulls had already been utilized and briefly diecussed by the author (’33) in his study on th- growth and development of the macaque. TABLE 16 Dental formulae of 315 macaques (Patheew) with at least part of the permanent dentition, arranged to show the sequence of eruption o f the permanent teeth INCOMPLETELY EBUPTED 17 69 6 3 22 17 20 23 iicmm iicmmM iicmmM iicmmM IicmmM iicmmM iicmmM IicmmM IicmmM IicmmM IicmmM IIcmmM IIcmmM IIcmmM IIcmmM IIcmmMM IIcmmMM IT1c m m M M IIcPmMM 4dand1P I I c m m M M IIcPPMM 5d IIcmPMM 19 IIcPmMM 4dand3Q L I C m m M M IIcmmMM IICPmMY IIePPMM 4d&nd1Q I I C P Y M Y " LXCEPTIONS (SINQW OASES) Cn 11cases 1. M1 [n 14 eases u. M1 In 3 easea u. I1 In 3 eases 1. I1 In 11cases u. 11,in'5of these cases 1. I1 In 1 3 caaes 1.12, in 3 of these cases u. I1 I n 16 cases u. 12, in 7 of these cases 1. I 2 I n 1 8 cases L M2, in 10 of thesc cases u. 12, in 2 of these cases 1. I 2 In 18 cases u. M2, in 4 of these cases a I2 iicmmM IIcmm M '. IicmmM i I c m m M b a c. IicmmM W. IIcmmMM IIcmmMM I I c m r n M M M w' IIcPmMM IIcPmMM IIcmPMM IIcmPMM IIcPruYsL I I C m P M M w*Q '- I n 5 eases u.p1 I n 4 e a s e s a P1; in 2 cases u. P2;in2casesLP2 In 6 cases 1. C, in 5 of these cases u.P1 I n 3 cases 1.C; in 2 cases 1. P1 I n 5 caws 1. C; in 1Q u. and 1. I I e P P M M P1 and P 2 I I C m P M M w* IICmmMM In 2 cases n. c; in 1case u. IICPmMM 2Q I I c P P M M w-Q IICPmMM and 1. P1 In 15 d a n d 4 Q u. C, in 12 of IICPPMM l8dand 2 3 p I I C P P M M these d 1. C I I C P P M M - I n 3 d and 12 Q 1. M3; in 6 d I I C P m M M and 17' I I C P P M M M I I C P P M M M'.Q 11C P P M M M I n 1 3 cases u. M3, in 5 of these cases 1.3f3: in 5 2 u. C I I CP PM M M I bE7 " 528 ADOLPH E. SCHULTZ on an average 3 months before the upper ones (table 2) and, according to Spiegel (’34, average of 6 specimens recalculated for calendar months), this difference is even 4 months. The Incisors are very soon followed by the M2, the lower ones appearing slightly before the upper ones (in 37 of the skulls and in 5 of 7 living animals). In all the living macaques and in all the skulls which permitted a decision in regard to this problem the deciduous molars were not shed and the replacing Premolars had not actually erupted until after the M2 had appeared. It will be shown later that some authors have claimed that the eruption of the Premolars precedes that of the M2 - a conclusion for which the writer has f o m d no evidence among his material which exceeds by far the series utilized by other investigators. The writer has examined the dentition in over 100 young macaques immediately after their death and again when the skulls had been returned from maceration, and thereby it was found that in many instances some deciduous molars may be held merely by the gum and one or two, partly resorbed, slender roots and might consequently very easily become lost after death, in which case the Premolars underneath might erroneously be regarded as erupting. The detailed order of appearance of the Premolars varies a great deal, occupying on an average a period of only 3 months. It can be stated, however, that, as a rule, the upper P1 erupt before any of the other .Premolars. The lower C follow immediately after all the Premolars have appeared and the upper C are added to the permanent dentition shortly afterward. In ’some instances the upper and the lower C can erupt simultaneously, but not a single case was encountered in which there was evidence that the upper C erupted before the lower C. I n Pithecus, as in so many other primate genera, the Canines of males erupt relatively later and somewhat more slowly than those of females (tables 2 and 15, column ‘Incompletely erupted’). The last permanent teeth to be added to the dentition of macaques are first the lower M3 and then the upper M3. That the former appear a considerable time before the latter is proved‘not only by the author’s ERUPTION AND DECAY OF TEETH IN PRIMATES 529 records on a living animal of known age and by Spiegel’s (’34) data on three other living macaques, but also by the fact that in a total of twenty-seven skulls only the lower, but not the upper M3 were out and that in eight additional skulls the lower M3 had completely erupted at a time when the upper M3 were only partly out. I n no skull was the reversed relation observed. I t is interesting to note among the ‘exceptions’ two cases in which the lower M2 had appeared before all of the Incisors and two other specimens in which the lower M3 had erupted before all the Premolars. These unusual cases resemble the condition prevailing in the Colobinae. Bolk (’26) was the first author to study the sequence of eruption of the permanent teeth in macaques. Without stating the number and distribution of specimens examined, he gives the following formula for the order of appearance of the teeth in the lower jaw of Pithecus irus (=‘Macams cynomolgus’): M1, 11, 12, M2, P2, P1, C, M3. This agrees exactly with the corresponding findings of the author (fig. 2). In a total material of sixty-three Pithecus rhesus, of which only an unrecorded part were skulls with incomplete permanent dentition, Krogman (’30) studied the order of eruption of the teeth, arriving a t the following conclusion : 1. M1, u. M1, - - u, 11, 1. 11, u. and 1. 12, -- u. P1,1. P1, u. P2, 1. P2, - 1. M2, u. M2, - u. and 1. C, - u. and 1. M3 (- =resting period). The most significant difference between this formula and the corresponding findings of the writer exists in the middle period of dental eruption, for which Krogman states that the Premolars precede the M2 and that there even elapses some time between the appearances of the former and of the latter teeth. Krogman’s conclusion finds support in the following formula for also Pithecus rhesus (=‘Macaca mulatta’), as stated by Marshall ( ’33) : Ml, 11 and 12, P1 and P2 (twenty-third to twenty-fourth month), M2 (twenty-eighth to twenty-ninth month), C, M3. It is not quite clear, however, exactly what Marshall meant by ‘eruption, and he mentions that “The available data on animals between two and four years are A X W C A X JOWNAL OF PHYSICAL AXTHBOPOIl)QY, POL. XIS, NO. 4 530 ADOLPH H. SCHULTZ somewhat fragmentary . . . .” The writer can merely repeat that his seemingly ample evidence forces him to disagree with the claims of the two last-mentioned authors that in macaques the Premolars erupt before the M2. This discrepancy cannot be explained as being due to some species difference, because the large majority of the specimens in table 15 are also of the species Pithecus rhesus. Furthermore, the recent investigations by Spiegel (’34) on living Pithecus irus have established the same sequence of eruption for this species as was found by the writer for Pithecus rhesus (table 2). Spiegel states specially that the Premolars do not appear until 1 to 12 months after the eruption of the M2. HIGHER PRIMATES The sequence’of eruption of the permanent teeth of gibbons (table 16) is practically the same as in the subfamily Lasiopyginae. The upper and lower I1 erupt simultaneously in most cases. All other teeth seem to appear, as a rule, slightly sooner in the lower than in the upper jaw. The Canines erupt before the M3 and somewhat earlier in females than in males. The latter difference is particularly noteworthy, in view of the fact that in Hylobates the Canines are of practically the same large size in both sexes. Huxley (1871) mentions that “ I n the Gibbons, the permanent canine emerges contemporaneously with, or before, the last molar.’’ Based upon his study of fifteen young skulls of Hylobates concolor, Kirchner (1895) gives the following sequence of eruption: 1. 11, u. 11, 1. M1, u. M1, 1. 12, u. 12, 1. M2, u. M2, u. P1,l. P1, u. P2, 1. P2,l. C, u. C, 1. M3, u. M3. The small number of cases examined may explain the erroneous conclusion of Kirchner that the I1 are the first permanent teeth to appear. With the exception of this reversed relation in the order of appearance of the I1 and the M1, and the claim that the upper Premolars appear before the lower ones, Kirchner’s formula agrees very well with the author’s findings (fig. 2). The latter are in general agreement with the following formula for Hylobates (and Symphalangus !) given ERUPTION AND DECAY OF TEETH I N PRIMATES 531 - by Krogman ( '30): u. and 1. M1, -- 1.11, u. 11,u. and 1. 12, u. M2,l. M2, - u. and 1. P1, u. and 1. P2, -- u. and 1. C, u. and 1. M3. This formula differs from the writer's results merely TABLE 16 Dental formulae of forty gibbona (Hylobates) with at least part of the permanent dentition, arranged t o show the sequence of eruption of the permanent teeth NUYBEB Or SPICIYENS DENTAL M B Y U L A INCOMPLETELY m U P T E D 1 .iemm .iemmM 1 iiemmM iiemmM 1 [icmmM iicmmM 4 IiemmM liemmM I n 3 cases u. and 1. I1 6 IiemmM LlemmM I n 1 m e 1. I 2 4 IIemml IlemmY I n 4 cases ILI 2 1 IIcmmM [IcmmMM 1. M2 3 IIemmMM IIePmMM In 3 c a m 1. P1 2d IIcPPMM IIePPMM I n 1 case u. P2 30 IIcPPMM IICPPMM I n 2 saseg 1. C 2 dand 1 5 IICPPMM IICPPMM In 1 dand 10 u. C ldand35 IICPPMM I n 1 0 u. C; in 1 d u. and 1. C, i x IICPPMMM both these eases 1. M3 4Jand25 I I C P P M M M In 6 eases u. C; in 2 d and 2 Q IICPPMMM u. M3 EXCEPTIONS ( S I N Q W OAeES) 1. M 1 IcPPMM Ic P P M M M . ' 532 ADOLPH H. SCHULTZ in regard to the relations between corresponding teeth in the two jaws and in regard to the occurrence and relative duration of the time intervals. The orang-utan (table 17) shows essentially the same order of appearance of the permanent teeth as the gibbon. Of the two (wild) ‘exceptions’ the first is of interest because, as in so many other exceptions, it demonstrates a tendency to retain some deciduous teeth for an abnormally long period. The second case is probably not a real exception at all, but shows that in some females the upper and lower C can erupt before all Premolars have appeared. Owen (1840 to 1845) and Nagitot (1869) are probably the first authors who have attempted to study the sequence of eruption of the teeth in anthropoid apes. The former author, after examining some skulls of young orang-utans, gives the following sequence of eruption for the teeth of this ape: M1, 11, M2, 12, P1 and P2, M3, C. He states specifically that (apparently in a living animal) the lower I 2 erupt 8 months after the upper M2. This, however, must be a very exceptional and probably abnormal occurrence. Magitot bases his conclusions upon an examination of the juvenile skulls of 3 orang-utans, 3 chimpanzees and 6 gorillas. Of this total of 12 specimens 7 possessed only the M1, whereas 3 had all permanent teeth, though not all completely erupted. This leaves only two specimens for the entire period, covering the eruption of all Incisors, M2, all Premolars and Canines! I t is not surprising, therefore, that later and better substantiated investigations did not support most of Magitot’s conclusions in regard to the order of appearance of the permanent teeth in the large apes in general. This order he states to be ‘‘absolument dans le m6me ordre que chez l’homme, c’est;-dire :” - M1, - I1 and 12, P1 and P2, C, - M2, - M3 - (- = terminating Magitot’s ‘periods of dental development’) . Huxley (1871) mentions that in the large apes, in contrast to the gibbons, “the last permanent canine is cut, ordinarily, only after the appearance of the last molar.” This statement, too, is not in agreement with the findings of later authors. ERUPTION AND DECAY OF TEETH I N PBIMATES 533 On a very considerable series (the total number of available specimens is not recorded) of young orangutan skulls Selenka (1898) has studied the sequence of eruption of the teeth. According to his tabulated data, the M1 are always the first permanent teeth to appear, to be followed by the lower I1 TABLE 17 Dental formulae of twenty-eight orang-utans (Pongo) with at leaat port of the permanent dentition, arrolrged to 8 h w the sequence of eruption of the permanent teeth INCOMPLETELY EBUPTED 'I 13 and 2 9 4'Md "11 iicmm iicmmM Iu 1 ease 1. Ml iiemmM iicmmM In 1 case u. M1 IicmmM IicmmM In 2 w IIemmMM IIcmmMM In 2 eases u. M2 ;in 1 case u. I2 IIcPmMM IIcPPMM 1. P1 IIcPPMM IIePPMM In 1 case 1. P1 IICPPMM I CP P M M In 3 'and 1 9u. and 1. C I1 iicmm MM C I c m P M M w' CICPPMM I: I C P m M M w'p IICPPMM In 2 enses u. C; in 1 case 1. M3 IICPPMMM 2g l' s u. and 1. I IICPPMMM u. and 1. C IICPPMMM in five cases and by the upper M2 in six other cases. The detailed order of appearance of the different Incisors and the upper and lower M2 Selenka found to vary a great deal, so that in quite a number of skulls the upper and (or) lower M2 seemed to have actually erupted before all the Incisors had appeared. This constitutes the chief discrepancy be- 534 ADOLPH H. SCHULTZ tween the results of Selenka on one side and those of Krogman, Keil and of the writer on the other. The appearance of all M1, Incisors and M2 is followed in all of Selenka’s cases-by the Premolars and Canines, the latter erupting in the great majority of the cases after the former. The M3 are recorded as the last normal teeth to erupt in all but one instance, in which the lower C had been delayed in their usual order of appearance. Selenka mentions also that supernumerary Molars erupt always after the usual permanent dentition has been completed. He distinguishes different phases in the process of eruption which are separated by intermissions of varying duration. The first of these intermissions follows the eruption of the M1, the second that of the Incisors and M2, and the third that of the Canines. Between the last two intermissions occur the third and the fourth phases of eruption which are described as follows (in free translation): “Third phuse. After a considerable intermission appear the anterior and posterior Premolars, in varying order, but in rapid succession. Fourth phuse. The Canines are added immediately, but they grow extraordinarily slowly in males.’’ According to the findings of Krogman and those of the writer, there exists no significant period of inactivity preceding the eruption of the Premolars, i.e., at the time for which Selenka claims his second intermission. Krogman (’30), who has studied a total of 134 orang-utan skulls (again it is impossible to find out in how many of these the permanent dentition is as yet incomplete), gives the following formula for the sequence of eruption of the teeth: u. and 1. M1, --- 1.11, u. I1,l. 12, u. 12, - u. and 1. M2, u. and 1. P1, u. and 1. P2, -- u. and 1. C, - u. and 1. M3 (- =relative time interval). This formula agrees in nearly all essential points with the corresponding results of the wfiter (fig. 2), the only and as such minor differences exist in regard to the detailed order of appearance of the Premolars and of some of the same teeth in the upper and in the lower jaw. Recently Keil ( ’33) has re-examined the Selenka collection of orang-utan skulls ( sixty-five young specimens), obtaining 535 ERUPTION AND DECAY OF TEETH I N PRIMATES TABLE 18 Dental formulae or eighty-aiz chimpawees (Pan) with part or the permanent dentition, arranged to show the . 9 e & ~ ~ eof eruption of the permanent teeth INOOMPLETILY EEUPTID LSOEPFIONS ( SINQm OASES) 2 iicmm iiemmM 33 iicmmM iicmmM 2 IicmmM IicmmM In 2 case8 u. 11; in 1case 1. I1 3 IicmmM IIcmmM I n 1case u. 11;in 1 m e L I 2 2 IIcmmM IIcmmM I n 1case u. I 2 2 IIcmmM IIcmmMM In 2 cases 1. M2 iicmmM iicmmMM 5 I I c in m M M IIcmmMM I n 2 cases u. M2 t-I-c P m M IIc-PM 1 IIcmmMM IIcPmMM 1. P1 and u. M2 11-PPY c. P 11--PMM 2 IIcPmMM IIcmPMM I n 1case u. P1 and 1. P2 IIcmmMM IIcPPMM 2 IIcPPMM I I e I? ni M M In 1case u. P1 and u. P 2 IIcPPMM IIcPPYM In 1case u. and 1. P1; in 1case u. P 2 IIcPPMM IICPPMM I n 2 cases 1. C, in 1 0 u. P1 IICPPMM IIcPPMM In 2 ages u. C IICPPMM IICPPMM In 1dand 3 ?u. and 1. C;in 29 u. c IICPPMM 1 I C P '1 M M M I n 1d a n d 1Pu. and]. Cand 1.M3 In 1m e 1. M1 In 6 cases u. M1, in 2 of these 1. M 1 C. C. IV' 536 DOLPH H. SCHTJLTZ the following formula for the sequence of eruption of the permanent teeth: M 1 - - I1 I2 M2 -- (P1 P2) - C -- M3. This formula agrees with the corresponding conclusions of Krogman and of the writer with the exception of the resting period after the eruption of the M2. The sequence of eruption of the permanent teeth of the chimpanzee (table 18) is, as a rule, practically the same as that of the orang-utan. I n captive specimens, however, there can occur a signillcant difference, consisting in the eruption of some of the Premolars earlier than some of the M2 (table 3 and ‘exceptions’ in table 18). Such an order of appearance of these particular teeth has not been observed by the writer in any wild chimpanzee and does not occur in all of the captive specimens. It seems that some consequences of captivity (rickets?) can in chimpanzees produce the occasional delay in the eruption of M2 or, possibly, an abnormally early shedding of molars, thereby facilitating an earlier appearance of the replacing Premolars. The long resting period in dental eruption, following after the appearance of the M1, is unmistakably indicated by the fact that in thirty-five of the eighty-six chimpanzees with incomplete dentitions the M1 are the only permanent teeth present. This resting period has actually been found to last considerably over 2 years (table 3). It is to be expected that a dental formula, remaining unchanged for such a long time, should be encountered in a much higher percentage of specimens than the formulae which undergo alterations in comparatively rapid succession. A sex difference in the relative time of eruption of the Canines, existing in many other primate genera, is not clearly defined in the author’s material of chimpanzees. Selenka (1899) gives in form of a diagram the following sequence of eruption of the permanent teeth of chimpanzee (only three skulls!) : u. M1, 1. M1, 1. 11, u. 11, 1. M2, u. 12, 1. 12, u. M2, 1. P1, u. P1, 1. P2, u. P2, u. C, 1. C, u. M3, 1. M3. I n two other skulls he found that the last six types of teeth appeared in the following, slightly different order: u. P2, EBUPTION AND DECAY OF TEETH I N PRIMATES 537 1. P2,l. C, u. C, 1. M3, u. M3. This agrees in most the major points with the corresponding results of the writer, the only essential difference consists in the early eruption of the lower M2 according to Selenka - a condition found by the writer in only one captive specimen and hence listed as an exception. Based upon his study of a series of twenty-seven chimpanzee skulls with incompletely erupted permanent dentitions, Zuckerman ('28) concludes that the usual order of appearance of the teeth is as follows: M1, 11, 12, M2, P1, P2, C, M3. This is in complete accord with the corresponding results of the writer (fig. 2). This particular sequence is furthermore supported in its major points by the report of Krogman ('30), who has studied a very considerable, though unnaxqed, number of young chimpanzee skulls, and summarizes his findings in the following formula: u. and 1. M1, --- u. and 1. 11,u. 12, 1. 12, u. and 1. M2, u. P2, 1. P2, u. and 1. P1, -- 1. C, u. C, u. and 1. M3 (- =relative time interval). The order of appearance of the permanent teeth of gorillas (table 19) is the same as that in the other large apes, except in the detailed sequence of eruption of the Premolars which has been found to be particularly .variable in all the primate genera investigated. Among the gorilla skulls examined there are thirteen in which the M2 are either at least incompletely erupted before any Premolar has appeared, or else they are completely out before the Premolars, which have appeared, have completed their eruption. I n not a single skull has the reversed relation been observed. This is specially mentioned, because Krogman has claimed that in the gorilla the M2 do not erupt until some time after all the Premolars have appeared. The data on the degrees of eruption support the conclusion that in the gorilla the large Canines of the males erupt slightly later and much more slowly than the small Canines of the females. Selenka (1899)' gives two diagrams for the order of appearance of the teeth of gorilla. The first, based upon only four skulls, shows the following sequence :u. M1,l. M1, u. M2,l. M2, u. 11, 1. 11, u. 12, 1. 12, 1. P1, u. P1, 1. P2, u. P2, u. c, 1. c, - 538 ADOLPH H. SCHULTZ TABLE ID Dental formulue of seventy-eight gorillas (Gorilla) with part of the permanent dentition. arranged to show the sequence of eruption of the permanent teeth INCOYPLITSLY SPUPTED EXCEPTIONS (S110QW CASES) 6 iicmm iicmmM I n 6 casea 1. M1 14 iicmmM iicmmM I n 1 case u. MI 3 iicmmM IicmmM I n 2 casee 1. I1 3 I i c in m M 11i c m m M In 1 case u. I1 1 IiemmM l'IemmM u. I1 and 1. I 2 2 ITemmM IIcmmM I n 1case u. I 2 1 IIcmmM LIcmmMM 1. M2 5 I Iem'm M M IIcmmMM In 2 cases n. M2 2 IIcmPMM IIcmmMM In 2 cases u. P 2 1 IIcPmMM IIcmPMM u. P1 and 1. P 2 3 IIcPPMM 11 I c m P M M I n 1case u. P1; in 2 eases u. and 1. PO 11-PmMM 11-PPMM 28and59 IIcPPMM IIcPPMM I n 3 cases 1. P1 IIcPPMM 11C P P M M M 11-PPNM IICPPMM In 2 cases 1. C; in 1 ease u. P2 IICPPMM I I c P P M M **' IICPPMM IICPPMM I n 2 d a n d 1On. and 1. C IICPPMM IICPPMMM I n 12 cases 1. M3 ;i n 6 6 u. and 1. c 29 2dand69 6 d and 7 91 I-cmmM W. iicmmM IIcmmMM I I c P m M M w* IICPPMMM IICPPMM lv- 0 ERUPTION A N D DECAY OF TEETH IN PRIMATES 539 1. M3, u. M3. The second and incomplete diagram, composed of the dentitions of only three additional specimens, gives the following sequence: 1) u. M1, 2) 1. M1, 3 ) u. 11, 4) 1. M2, 5) u. M2,6) 1.11, . . . . 13) 1. C, 14) u. C, 15) u. M3,16) 1. M3. One wonders whether Selenka regarded an M2 as ‘erupting’ when merely visible in the depth of its open alveolus, or whether he has had to estimate the relative order of eruption of the M2, since his far too small series may have lacked the necessary stages showing the actual, normal order of appearance of these particula’r teeth. It is interesting to note that Selenka considers the M2 the second (upper and lower) teeth to appear, whereas the writer assigns them to the fourth place and Krogman even to the sixth! Virchow ( ’20) mentions that in the gorilla (two specimens) the M2 erupt before the Premolars. Krogman’s (’30) formula for the sequence and rate of eruption of the teeth of gorilla, derived from his examination of a very considerable material (actual number of skulls unrecorded), is here transcribed as follows: u. and 1. M1, --- u. and 1.11, u. and 1. 12, - u. and 1. P2,l. P1, u. P1, - u. and 1. M2, -- 1. C, u. C, ‘or’ u. and 1. M3. As mentioned above, the writer is forced t o disagree with this formula chiefly in regard to the order of eruption of the M2, and also in regard t o the reversal in the order of first appearance of the Canines and the M3. That the M3 may erupt simultaneously with, or even slightly earlier than the Canines is admitted as a possibility for an exceptional caae (table 19, ‘Exceptions’), but never as a sufficiently frequent occurrence to constitute a tppical condition. The sequence of eruption of the permanent teeth of man, as shown diagrammatically in figure 2, is based upon the data assembled in table 4, which represent a general average condition for the recent races of the genus Homo. As in nearly all the other primates, in man the permanent dentition starts with the eruption of the M l and is completed with the appearance of the M3, but the middle order of eruption differs from that of all other primates in several very significant respecfs. The Incisors follow the appearance of the M1 without any 540 ADOLPH H. SCHULTZ resting period, the Premolars and Canines erupt early, and the M2 unusually late. According to table 4, the average ages of eruption of the lower I1 are in many instances the same as the average ages of eruption of the upper M1. It is to be expected, therefore, that individually the former teeth can frequently appear even somewhat earlier than the latter teeth, and such a relation does, indeed, constitute another unique condition among all primates. PHYLOGENETIC CHANGES I N SEQUENCE O F ERUPTION O F TEETH I n view of the extreme scarcity of information in regard to the sequence of eruption of the teeth in mammals besides the primates and the complete lack of data for the suborder of prosimians, it is as yet impossible to decide which general type of sequence represents a primitive and original condition and which other types must in consequence be regarded as phplogenetic specializations. As a mere working hypothesis, however, it may be assumed that the most primitive sequence of eruption consists in an initial simple addition of teeth ( M l , M2 and M3) of the second generation to those of the first generation and only subsequently in a replacement of deciduous teeth by permanent ones, and this beginning with the I1 and 12, followed by the various Premolars, and ended with the Canines. With advancing specializations of the primates appeared a trend toward marked prolongation of the period of individual growth, so that the deciduous teeth would have had to function for steadily increasing periods if their replacement had not gradually become shifted to progressively earlier places in the entire order of appearance of the permanent tee’th. If this hypothesis is tentatively accepted as plausible and as not contradicted by known facts, the formulae assembled in figure 2 can be interpreted in the following manner (fig. 3) : All the primates investigated have retained at least a part of .the hypothetical, original sequence of eruption of the permanent teeth, this part consisting in the initial addition of the M1. Saimiri and Pygathrix adhere still further to the primitive formula by adding next the M2. 541 ERUPTION AND DECAY OF TEETH IN PRIMATES I n the other genera this second step has become delayed by the accelerated beginning of the replacement of deciduous teeth which, however, starts in the assumed original order, i.e., with the 11, followed immediately by the I2 (except in Colobus in which the M2 follow the 11). After this newly acquired, early appearance of the Incisors there occurs a return to the primitive condition of adding, rather than replacing, teeth in all the primates, except man. I n Pygathrix all M3 are being added, in Saimiri at least the lower M3, and HYPOTHETICAL ORIGINAL FORMULA PY6ATHR'Xs SAlMlRl (L.JAW) y' y2 A, A 2 4 COLOBUS MI ?IM* c HOMO $ M< >I2 Tp 14Gh iP 4 It PP / ;5 5 i2 F M y l o - 4 /I2 P C P M2 SEQUENCE OF ERUPTION M4 14 c' I - h +I Fig.3 Condensed and generalized representation of the different degrees of evolutionary change in the sequence of eruption of the permanent teeth in primates. The unaltered order of appearance of a tooth is indicated by a perpendicular arrow, a shifting in this order by a diagonal arrow. in the other monkeys and apes all the M2. I n man alone has the original order of eruption become even more specialized at this point, inasmuch as the addition of the M2 is postponed until the deciduous molars and canines have been replaced. The primitive, rapid addition of the M3 has become relatively retarded in all primates, but decidedly less so in Pygathrix and (regarding the lower M3) in Saimiri than in any of the other genera. This is due to the comparatively early replacement of the molars and canines. The order in the latter replacement follows in all monkeys and apes in general the primitive formula, i.e., the Premolars appear 542 ADOLPH H. SCHULTZ before the Canines. In man, on the other hand, even this sequence has become changed, inasmuch as particularly the lower Canines erupt frequently before all Premolars have appeared. These considerations lead to the hypothetical and general conclusion that the sequence of eruption of the permanent teeth is most primitive in Saimiri among the platyrrhines and in Pygathrix among the catarrhines and that it is most specialized among all primates in the recent representatives of the genus Homo. I t is of great significance in this connection that, according to Virchow ( 'ZO), in the fossil child of Ehringsdarf the M2 erupt before the P1 and P2, and not afterward as in modern man.' The human specializations consist in the rapid succession in eruption of the M1 and 11, in the complete replacement of the deciduous dentition before the M2 are being added to the permanent dentition, and in the appearance of the lower C before at least the P2. I n other words, it is unquestionably a new and exclusive aquisition of man that his M2 erupt comparatively late and his Premolars and, particularly, Canines relatively early. I t is perhaps more than a striking coincidence that this comparatively 'premature' appearance of the Canines of man is associated with a relative size of these teeth which is so markedly smaller than in any other primates of at least the male sex. These conditions are shown diagrammatically in figure 3, where it is seen that any shifting in the order of appearance of the teeth which are being added to the dentition (Molars) proceeds from left to right, whereas all shifting in the general sequence of eruption of the teeth which replace the deciduous dentition takes place in the opposite direction, i.e., from right to left. Figure 3 shows also very clearly that in man alone becomes the deciduous dentition completely replaced by permanent teeth before the M2 are being added to the dental arches. I n the large majority of the primates the process of replacement is interrupted, instead of followed, by the 'Spiegel ('34) has recently called attention to the fact that the picture by GorjanoviE-Kramberger ('06) of the fossil human mandible ' C ' from Krapina ehowa an erupted M2 alongside an m2 (and not a P2). ERUPTION AND DECAY OF TEETH IN PRIMATES 543 addition of M2. I n conclusion it must be emphasized that in regard to these conditions the large apes fall into one group with the majority of the monkeys and are sharply separated from man. This is not the place for following the temptation to speculate on the possible tames and consequences of this highly specialized sequence of eruption of the teeth of man. It may be pointed out, however, that in man the tremendous and unique lengthening of the duration of postnatal growth, accompanied by corresponding increases in the ages of dental eruption, has brought about a dangerously long period of functioning for the deciduous teeth without any improvement in the durability of the substance of these teeth. If the completed replacement of the deciduous dentition had to wait in man, as in other primates, until after the addition of the M2, the life span of some of the milk teeth would have to be lengthened by several years, even though this span is on an average already more than twice as long in man as, e.g., in the macaque. CORRELATIONS BETWEEN ERUPTION AND ATTRITION OF TEETH AND CLOSURE OF SOME CRANIAL SUTURES As mentioned in. the chapter on Explanations, for each skull the state of attrition of the teeth and the ectocranial closure of two of the sutures has been recordecl and this, chiefly, for the purpose of classifying the material according to age. I n the first age group, containing all specimens with incompletely erupted permanent dentition, noteworthy attrition of the teeth is rare. In skulls still lacking the M3 one can observe occasionally a slight degree of wear on the M1 and the I1 and in a few cases even on the I 2 and the C. Such premature attrition of teeth among ‘young’ specimens occurs somewhat more frequently in the large apes and the gibbons than in the lower primates. Among the latter it has been observed in a total of only six cases in the entire material of ‘young’ platyrrhines. 544 ADOLPH IT. SCHULTZ As a rule, the base suture and the sagittal suture are (at least partly) open during the entire period of dental eruption. The following exceptions to this rule have been noted in the material listed in tables 6 to 19, and referring invariably to specimens from the last two rows of these tables, i.e., to the very oldest specimens with incompletely erupted dentitions : Gmus Gorilla Hylobates Pithecns Colobns XpccimsM with dosed Bore ruture 8agittal ruturd 2 4 0 5 3 2 0 2 After the completed eruption of the entire permanent dentition, the attrition of the teeth becomes rapidly more noticeable with advancing age, beginning generally on the teeth with comparatively early ages of eruption, i.e., the M1 and the Incisors, though the Canines are also among the first teeth to show marked signs of wear in a considerable percentage of the cases. I n practically all primates the M2 become worn only after attrition is clearly recognizable on the M1, Incisors and Canines, but before it is seen on the Premolars and the 343. In many old specimens it is observed that the Incisors and Canines have become reduced to mere stumps, the crowns of these teeth having nearly or entirely disappeared, and yet the M3 and at least some of the Premolars show but a moderate degree of attrition. I n even more extreme cases all teeth can be worn to the gums. Such extremes have been found with surprising frequency among the higher primates, they are slightly less common among lower catarrhines, and they did not occur among any of the platyrrhines examined, except in the genus Ateles. The percentage distribution of the degrees of dental attrition and of the closure of cranial sutures in primates with completely erupted dentitions is shown in table 20. The data in this table are of manifold interest, but will be discussed very briefly and without considering the sequence of suture 545 ERUPTION AND DECAY OF TEETH IN PRIMATES closure or the literature on the latter problem.6 In contrast to the lower primates, the higher forms contain generally very few specimens in which both the base suture and the sagittal suture are still open after all the permanent teeth TABLE ao The correlations between the degree of attrition of the teeth and the closure of two of the cranial sutures in specimens with oompletely erupted permanent dentition. The pgures represent the percentages of specintau showing particular colnbinutions in these conditions Open QINUS TOTAL IUYBEB OP IXULLS Gorilla 245 Pan 126 67 Pongo 130 Hylobates 227 Pithecua 68 Papio 134 Lasiopyga 59 Colobus 41‘ Nasalis 273 Pygathrix 158 Ateles 105 Cebus Alouatta 210 Saimiri 48 OcdiDomidar 35 Mean I (1926) I ClOSed Open Ilight - Jlight Mu& Bdult Adult Adull 4 12 6 2 25 22 62 31 51 26 32 45 19 69 11 28 -- .. .. .. .. 6 .. 5 .. 2 2 1 1 -18 34 9 1 7 7 .. 3 5 14 0.4 .. 3 .. 5 3 .. .. 7 5 .. .. .. .. .. 1 .. .. .. .. .. 1 slight .. 6 1 2 0.8 11 .. 6 7 2 7 27 ’ BASE SUTUBB Clmd Much .. 2 .. .. Blight Much Adult Old 3R 39 36 32 49 30 44 10 9 27 32 3 8 35 -37 25 42 7 19 2 25 13 3 14 5 3 5 5 2 14 37 27 12 33 1 2 13 30 17 14 3 11 72 -15 8 16 .. BAQITTAL SUTlJm -- .. .. D=QBP= or ATTRITION O r TIPTH AQE .. 3 21 have completely erupted. Only 2 per cent of the gibbons, 4 per cent of the gorillas, 6 per cent of the orang-utans, and 12 per cent of the chimpanzees have both the sutures still open. In none of these specimens do the teeth show ‘much’ 61t must be emphasized that, as stated under ‘Explanations,’ a suture is here considered to be closed only when at least three-foiirths of its length have become entirely obliterated. The selection of this definition for the present purpose may in part explain certain apparent discrepancies between the results of the writer and those of hrogman (’30), who has studied in great detail the suture closure in anthropoids, macaques and baboons. 546 ADOLPH H. SCHULTZ wear. I n lower primates, on the other hand, ‘much’ wear does occur, though rarely, among the high numbers of adults with both sutures still open. Even if the sagittal suture is already closed, ‘much’ wear is found but rarely as long as the base suture is still open, namely, on an average in only 2 per cent of the specimens. The orang-utan stands out among all the genera examined as the primate with by far the highest percentage (37) of cases showing the combination of closed sagittal and open base suture and as the only primate in which the reversed combination could not be observed. I n Oedipomidas, on the other hand, not a single specimen showed the former combination, whereas the latter was encountered in 83 per cent of the cases. With the exception of Alouatta, platyrrhines are characterized by the very late, and hence rare, closure of the sagittal suture. The gibbons are distinguished by having the highest percentage (91) of adult and old specimens with both sutures closed; gorillas (77) and chimpanzees (73) rank next in this respect, to be followed by Alouatta (65), Papio (63), and Pongo (57). I n the remaining genera these percentages are much smaller, reaching their lowest values in Ateles (3) and in Saimiri (0). Even after both sutures have become closed, the teeth are not or only ‘slightly’ worn in mostly very considerable percentages of the cases of nearly all the genera. It is, however, the group of skulls with obliteration of both sutures which shows on an average the highest percentage (24) of cases with ‘much’ wear of the teeth. This average percentage of cases showing ‘much’ wear decreases to 8 if only the base suture is closed, and to 1 if neither of these sutures has as yet become obliterated. DEVIATIONS FROM THE NORMAL CONDITIONS OF THE PERMANENT DENTITION I n the course of the examination of the permanent dentitions of primates a very considerable number of records accumulated, showing the frequency with which different variations in size, number and position of certain teeth occur ERUPTIOX AND DECAY OF TEETH IN PRIMATES .. .. .. .. 2 : :$ 9 m or( - k *rl .. .. .. .. .. .. AYPRICAN JOURNAL Olr PHYSICAIA ANTHROPOLOGY, VOL. XIS, NO. .. .. .. .. 4 547 548 ADOLPH H. SCHULTZ in the various genera. Special attention was also paid to crowded and impacted teeth and to abnormally long retained deciduous teeth. The percentage frequencies of these deviations from the normal conditions are listed in table 21. Striking reductions in size are found chiefly in the 113, but occur also, though very rarely, in other teeth. Thus, the upper I2 are vestigial in one gorilla6 and in one Oedipomidas; in one macaque a rudimentary Canine was encountered and in one gibbon and one baboon a P1 is clearly of diminutive size. Abnormally small M3 with reductions in the number of cusps Fig.4 Upper jaw of Alouatta palliata left M3. 0 w. (A. S. 777)' showing vestigial and of roots are quite common among gibbons, as has already been convincingly demonstrated by a number of investigators (Schultz, '33). I n all other catarrhines (besides man and gibbon) rudimentary M3 are extremely rare, having been found in only one chimpanzee and one macaque. In platyrrhines, 011 the other hand, striking rediictions in the size of the M3 (fig. 4) occur in all genera, manifesting a general trend toward the elimination of these teeth, an elimination which has already been accomplished in Oedipomidas and all other Callithrichidae. The most extreme reduction in size, i.e., the complete absence of one or more M3, is also very This specimen has been pictured in another paper by the author ( '32, fig. 1). Rudimentary upper I2 in another gorilla are mentioned by Regnault (1893). EIlUPTION AND DECAY OF T E E T H I N PRIMATES 549 rare in lower catarrhines, fairly rare in the large apes (only in 3 chimpanzees and in 1 orang-utan?), but quite frequent in gibbons. Among the latter &I3are missing in 5 out of 130 specimens examined by the aut,hor and in 2 out of 68 specinlens (adult Hylobates concolor) examined by Kirchner (1899). I n the New World genera Ateless and Cebus the congenital lack of M3 is much more frequent than in any other primate genus, except Homo. I n man one or more M3 are undeveloped in as much as 19 per cent of the cases (de Terra, ' l l ) , though some recent studies have resulted in smaller frequencies ; e.g., Fig. 5 Upper jaw of adult &bus unicolor tal lack of both M3. 9 c. (P. A. L. S l ) , showing congeni- according to Goblirsch ('30), one or more h13 were seen to be lacking on roentgenograms of 2112 adult white patients in 9 per cent of the cases. In extreme cases, as shown for instance in figure 5, even the M2 of platyrrhines may bear signs of marked reduction. That the complete suppression of M3 is a hereditary character in man has been demonstrated 'Bateson (1691) has reported the congenital lack of the upper r. M3 in an orang-utan and Briihl (quoted by Zuckerkandl, 1896) nientions another orang-utan skull with the complete absence of both upper M3. Buteson (1894) records the congenital lack of M3 in 3 out of 60 Ateles skulls. He did not encounter any such cases among the adult skulls of 66 Cebus and of 81 Alouatta. A series of pictures, showing different variations regarding the reduction in size of the M3 in Ateles and in Cebus have been published by the author ('25) i n a former paper. 550 ADOLPH H. SCHULTZ by a pedigree published by the author ('34). That it is of a hereditary nature also in monkeys, appears probable, in view of the fact that in the species Ateles geoffroyi the M3 were found to be congenitally lacking in 3.5 per cent of the author's series from Chiriqui, Panama, whereas in 15.4 per cent of the specimens collected in one locality in eastern Nicaragua. The addition of fourth Molars, o r the manifestation of an increased developmental activity at the aboral ends of the dental laminae, occurs with surprising frequency in the large apes, but is rare in man, gibboiis, and most lower primates. I n the series studied by the author one or more M4 were observed in 14 gorillas (138 and 1 9 ; 12 times upper and 2 times lower jaw; in 7 cases bilateral and in 7 cases nnilateral occurrence), 4 chimpanzees (18 and 3 0 ; 2 times upper and 2 times lower jaw; in 2 cases bilateral and in 2 cases unilateral occurrence) and 4 orang-utans (48 ; 1 time upper, 2 times lower, and 1 time upper and lower jaw; in the last case also lower r. M5;9 in 2 jaws bilateral and in 3 jaws unilateral occurrence). In the large series of 194 adult orangutan skulls of Selenka (1898), M4 are present in 19.6 per cent of the cases ( 8 25 per cent,lo P 15 per cent). According to the latter author (1899),M4 occur in gorillas in about 8 per cent of all cases, whereas in chimpanzees they have not been observed in his extensive experience. I n man M 4 are encountered sporadically and probably in no race more frequently than in aboriginal Australians among whom they have been found in 1.5 per cent of the cases (Campbell, '25). I n contrast to the large apes, the gibbons show M4 extremely rarely, only one such case having been observed by the author in a series of 130 specimens. Kirchner (1895)reports another case in a Hylobates concolor, encountered in a series of 68 ' A picture and brief description of this extreme case has been given h a paper by HrdliEka ( '07). Additional cases of M4 in skulls of the three large apes have been listed by Bateson (1894). '"Duckworth ('15) makes the incredible assertion: in the orang-iitan the frequency of occurrence (of M4) in the male sex amounts to nearly 50 per cent . This statement is based on the examination of the very large collection (i.e., the Selenka collection). (more than 200 crania) at Munich ". . . . ... . . . ." ERUPTION AND DECAY OF TEETH IN PRIMATES 551 adult, gibbons. Bateson (1894) did not find M.4 in a material of 51 gibbons. By combining these three series, it can be stated that M4 are found among 249 gibbons in only 2 instances, or in 0.8 per cent of the cases. I n the lower primates well-developed M4 are present in only 2 macaques, 1 guereza, and 2 spider monkeys (fig. 6). Bateson (1894) records supernumerary Molars in a baboon and a macaque among 419 Old World monkeys examined, and in 2 capuchins, 3 spider monkeys, and 1 howler among 284 (or more?) New World monkeys of the family Cebidae. Though the writer did not encounter M 4 in any Papio, Shaw (’27) found these teeth in 3.6 per cent of 112 south African baboons (probably P. porcarius). Fig. 6 Lower jaw of Ateles geoffroyi M4 on both sides. 9 w. (A. S. 1005), showing well-developed The real congenital lack of upper I 2 was observed in only 2 specimens, a gorilla and a gibbon. In man this lack occurs in over 2 per cent of whites (Schultz, ’34) and is a hereditary character. The congenital absence of lower 11, on the other hand, is rare in man, but fairly common among apes and monkeys (table 21). It is particularly frequent in howlers, among which it is found in 7 Alouatta palliata” and in 1 One of the cases is i l h t r a t e d in another paper by the author ( ’25, fig. 16). I t may be mentioned here that Ruffer (’20) has stated: “Absence of the first left mandibular incisor must have been fairly common in Lower Egypt, as four such cases have been observed in ancient Alexandria skulls.” 552 ADOLPH H. SCHULTZ A. villosa (5 8 and 3 0 ; 5 times left 11, 1 time right 11, and 2 times both I1 lacking without leaving any diastema). Congenitally missing Premolars were not encountered among the higher primates, but occurred in catarrhine as well as platyrrhine monkeys in a total of 7 cases. I n all these cases the lack is unilateral, in 5 cases a P1 is missing, and in the remaining 2 cases a P2. Invariably there is no space between the adjoining teeth in place of the missing Premolar, as demonstrated, e.g., by figure 20 in the author's ('25) former paper on this subject. Supernumerary Premolars were observed in the entire material in only 2 cases, a howler and a chimpanzee, both of which possess an additional, well-formed Premolar on one side of the lower jaw. Bateson (1894) has recorded the occurrence of supernumerary Premolars in a Brachyteles, an Ateles, and an Alouatta, and Wegner ('08) has described this anomaly in a Symphalangus. The only other numerical variations in teeth among the specimens examined 'by the author are the following cases: Additional Incisor in upper jaw in one gorilla, in lower jaw in another gorilla, an orang-utan, and a squirrel monkey. Incomplete twinning of tooth, i.e., doubling of crown, of upper I 2 in a guereza and of lower I1 in a howler. Apparently congenital lack of one Canine (with I 2 touching P1) in a macaque and in a capuchin. Cases of supernumerary Incisors in monkeys and apes have also been reported by Bateson (1894) and by Wegner ( '09). Positional variations of the permanent teeth of primates have been studied in great detail on a very large material by Colyer ('19 and '31). It suffices here, therefore, to give the author's corresponding observations merely in the condensed form of percentage frequencies with which the two most common positional variations were met with (table 21) and to discuss these very briefly. The percentages of specimens with one or more Incisors protruding strikingly beyond the others on account of crowding of the Incisors are listed in two of the columns in table 21. Two such cases are shown by excellent photographs in the figures 160 and 161 of the ERUPTION AND DECAY OF TEETH IN PRIMATES 553 book by Colyer ('31). A slight, though quite evident, degree of crowding among the Incisors, such as is shown in the lower jaw of a chimpanzee in figure 8, is surprisingly common in most genera and has not been included among the cases listed in table 21. A high degree of crowding, leading to marked and abnormal protrusion of one or several Incisors, is generally more frequent in the upper than in the lower jaw. It Fig. 7 Upper jaw of young Ateles geoffroyi ing of right Y3. Fig. 8 Lom?er jaw of young chimpanzee of right P2. 9 2 w. (A. S. 975), showing crowd- c. (P. A. L. 112), showing crowding 554 ADOLPH H. SCHULTZ affects the I1 much more commonly than the 12. Such crowding of Incisors is particularly frequent in the langurs, among which it occurred (in the upper jaw) in fifteen specimens, belonging to five different species. Marked crowding, accompanied by displacement, of Premolars is not at all a rare finding among wild or captive apes and monkeys. Figure 7 illustrates a moderate degree of this abnormal condition. Crowding in the Premolar region with- F i g . 9 Upper jaw of Papio hamadryas of right P2. d w. (A. 5. l68), showing twisting out pushing a tooth out of its proper alignment, but with wedging the tooth between its neighbors, thus keeping it from full eruption, was encountered only in two captive chimpanzees of which one is shown in figure 8, in one captive macaque, and in one wild capuchin. The first mentioned type of crowding of Premolars is, on an average, three times more frequent in the upper than in the lower jaw. I n the 48 specimens in which an upper Premolar had been crowded out of its proper place it had been pushed lingually 41 times, whereas labially only 7 times. On the other hand, in the 13 specimens with ERUPTION AND DECAY OF TEETH IN PRIMATES 555 crowding of lower Premolars the displacement occurred lingually 2 times and labially 11 times. The crowding affected the P1 in 29 per cent, the P2 in 56 per cent, and the P3 in 15 per cent of the cases with crowded Premolars. In 27 of the 61 specimens with crowded Premolars the corresponding teeth on the right and the left side of the jaw were pushed out of place, in 2 other specimens a P1 and a P2 on only one side of the jaw showed the crowding, and in the remaining 32 specimens only one of all the Premolars was affected. In four skulls of Alouatta palliata the bilateral, lingual displacement of upper P1 is very clearly caused by the ab- Fig. 10 Upper jaw of old Ateles geoffroyi d w. (A. S. 1009), showing impacted left C (and fully erupted, partly worn, right C). normal retention of the m l ; one of these cases is illustrated in figure 11 of a former paper by the author ('25). I n the majority of the cases of displaced Premolars, however, the abnormal position appears to be caused directly by a disproportion, no matter how slight, between the size of the jaw and that of the dentition. In a number of other instances a displaced Premolar is also markedly twisted, thus occupying more space sagittally than if standing in a normal direction. A moderate rotation of, chiefly, P2, as shown, for instance, in figure 9, is quite common among apes and monkeys-a fact which has been convincingly demonstrated by Colyer ('31). This frequent condition of rotation is, however, not necessarily 556 ADOLPH H. SCHULTZ correlated with the much rarer occurrence of actual displacement of Premolars. It remains in this chapter to discuss very briefly the frequencies with which impacted permanent teeth and retained deciduous teeth have been found among apes and monkeys (table 21). Impacted teeth were encountered in a total of 24 adult or old specimens (22 w.+ 2 c.). I n only 1 instance was an Incisor impacted, in 6 cases a Canine (fig. lo), in 7 cases a Premolar (in 2 instances due to the abnormal retention of the corresponding molar), in 5 cases an M3, and in the remaining 5 cases one or two b14. The chimpanzees show the highest frequency (5.6 per cent) of cases with impacted Fig. 11 Lower jaw of Pithecua rhema (and worn) right i l and lack of 11. 0 e. ( A . S. 1168), showing retained teeth, but in man such cases are even more common. According to a recent study by Mead ( '30), on a total of 6389 roentgenograms and skulls of different- human races, impacted teeth are found in man, on a general average, in 7.9 per cent of the cases (whites alone =12.7 per cent), but of all impactions in man 94 per cent appertain to M3 and only 6 per cent to all the other teeth together. Retained deciduous teeth in fully adult apes and monkeys are rarer than impacted teeth. The former occurred among platyrrhines only in the genus Alouatta, 4 adult, wild specimens having failed to shed their upper ml, and 1 specimen its upper il. Among catarrhines deciduous teeth were retained abnormally long in 13 specimens (table 21), of which ERUPTION AND DECAY OF TEETH I N PRIMATES 557 only 3 are captives. I n the entire group of these cases a total of 12 incisors (i i l 5 i2), 3 canines, arid 16 molars (‘7 m l 9 m2) was retained, 19 of these teeth belonging to the upper jaw and the remaining 12 to the lower jaw. I n the case of 10 (7 i, 1c, 2 m2) of these retained deciduous teeth (belonging to 7 specimens), the corresponding permanent teeth were congenitally lacking. One such instance is shown in figure 11. I n 5 cases (2 c 3 m2) of retained deciduous teeth, the permanent teeth, which should have replaced them, were impacted. The 7 abnormally long retained m l and 1 of the retained m2 caused the corresponding Premolars to be pushed out of their normal position. The data presented in this chapter furnish abundant proof for the general conclusion that congenital and developmental irregularities in the dentition are f a r from being restricted to man, occurring with varying and at times very considerable frequency among apes and Old as well as New World monkeys and this in captive and in wild specimens. + + + DESTRUCTION O F THE TEETH AND OF THE ALVEOLI AND LOSS O F TEETH The previous chapters have dealt chiefly with the beginning and middle periods in the life of the teeth of primates and have described the eruption, attrition, and developmental irregularities of the teeth. This final chapter is devoted to the problems of the decay and loss of teeth and of the destruction and dosure of alveoli. The chief emphasis is here placed not on the details of the dental pathology, but on the relative prevalence of the more or less extensive breaking down of the dental apparatus in the various groups of primates. F o r every skull examined was recorded the occurrence of dental caries, of manifestations of alveolar abscess, and of the complete loss of one or more teeth, followed by the disappearance of the corresponding alveoli. A tooth is here called ‘carious,’ if it contains a more or less extensive and irregular cavity, caused by the progressive destruction of 558 ADOLPH H. SCHULTZ Fig. 12 Lower jaw of Pithecus rhesus cavity in left M1. e. (P. A. L. 78), showing carious Fig.13 Lower jaw of young Papio sphinx c. ( A . S. l65), showing caries in both M1. ERUPTION AND DECAY OF TEETH I N PRIMATES 559 dental tissue. As a rule, caries in primates is readily distinguished from the effect of localized attrition and of erosion. In some instances, however, in which bhe crown of a tooth (mostly Molars) had apparently broken during the life of Fig.14 Lower jaw of Cebus capucinus 9 w. (A. S. 858), showing caries in both M1. Fig. 13 Upper jaw of young Pithecua rhesus in both 11. 9 c. (A. S. 1164), showing caries its owner, it seemed doubtful whether this happened in coilsequence of a previously existing carious cavity or was exclusively due to some other cause, such as traumatic injury. N o such uncertain case was included among the records on 560 ADOLPH H. SCHVLTZ caries. Examples of carious cavities in the dentitions of monkeys are shown by the figures 12 to 17. Many other excellent pictures have been published by Colyer ( ’31), who has discussed caries in primates in great detail without, however, considering the age changes in the frequency of caries. As ‘abscess’ was recorded every clear incidence in which any visible part of the alveolar walls or the adjacent cranial Fig.16 Skull of Saimiri orstedii w. (A. S. 877), showing caries on neck of right 11 (left I2 lost and alveolus closed). Fig. 17 Skull of Pitliecus rhesus 0 c. (P. A. L. 132), showing alveolar abscess above P1 and caries on the neck of P 1 and P2. ERUPTION AND DECAY OF TEETH IN PRIMATES 561 structures showed unquestionable signs of pathological destruction of the bony tissue, having originated in connection with the dentition. It is evident, therefore, that several different conditions are here combined under the general term Fig.18 Lower jaw of Gorilla gorilla ,j’w. (P. A. L. 13), showing extensive abscees formation on alveolus of right C. Fig. 19 Skull of Cebus capucinus w. (A. S. 963), showing extensive abscess in alveolus of right C and loss of this tooth before death of animal. ‘abscess. ’ Many cases represent so-called dento-alveolar abscesses, following frequently after the exposure of a pulp cavity through attrition, caries (fig. 17), or fracture of a tooth. In other, though rare, cases some mechanical force exerted on a perfectly sound tooth may have fractured the alveolar 562 ADOLPH H. SCHULTZ wall and thereby opened a way for suppuration of the tooth socket. Thus, the powerful Canines of many male primates could break the alveolar wall, before the tooth itself breaks, in case the tooth becomes wrenched labially while employed in fighting (figs. 18 and 19). Bone lesions on the alveolar walls of sound teeth develop in many primates as a consequence of paradontal disease which in turn originates most commonly from injury to the gums caused probably by food, as has been discussed in detail by Colyer ( ’31). Fig.20 Upper jaw of Gorilla gorilla abscess on right M1. d w. (P. A. L. 13), showing alveolar Examples of the pathological destruction of the alveolar walls in primates, spoken of below simply as ‘abscess,’ are shown in the figures 17 to 20. Further examples have been published in a previous paper by the author ( ’25 ; figs. 29 and 30) and four other cases are illustrated in the book by Coiyer ( ’31; figs. 135, 136 and 144). After the complete loss of a tooth its alveolus becomes gradually closed and the corresponding portion of the alveolar process may become resorbed. The data on ‘closed alveoli’ have been collected chiefly for the purpose of demonstrating the frequency with which monkeys and apes can outlive a t least part of their dentition and this even in the wild state. ERUPTION AND DECAY OF TEETH IN PRIMATES 563 The highest number of lost teeth in a single specimen was found among higher primates in a wild adult chimpanzee with 18 of its alveoli closed and among lower primates in a wild adult capuchin with the alveolar process for 13 of its teeth completely resorbed. That the loss of teeth and subsequent closure of their sockets is very rarely due to exclusively traumatic conditions, but is most commonly caused by some preceding disease process, appears highly probable. For instance, among the 18 chimpanzees with the alveoli of one or more teeth closed there exists abscess formation on other teeth in 15 specimens and in addition caries in 7 of the latter cases. By far the highest numbers of abscesses for sipgle specimens are found among gorillas and chimpanzees. The record among the latter is held by a wild, old female with abscesses on 17 of her teeth, and among the former 18 abscesses are present in a wild, old male (G.gorilla) and 16 abscesses in each of two other wild males (1G . gorilla, old and 1G. beringei, adult). In all the other genera this number never exceeds 10 and in only two instances 8. On deciduous teeth caries and abscess is found very rarely and only in captive specimens. Thus, caries of deciduous teeth was observed only in 3 captive macaques and abscess formation on the alveoli of deciduous teeth only in 1 captive capuchin, 8 captive macaques, and 4 captive chimpanzees. These cases, appertaining to the deciduous dentition, are omitted in tables 22 to 27 and in the discussion to follow. Caries of permanent teeth and abscess on the alveoli are very rarely seen in primates with incompletely erupted dentitions. I n the entire material of 982 young primates caries was observed in only 1 wild and 4 captive specimens and abscess in only 3 wild and 2 captive specimens. A closed alveolus, following the loss of a tooth, was never seen among the young primates examined. After the completion of the eruption of all permanent teeth and with the progress in attrition caries, abscess and loss of teeth become rapidly more frequent. This is abundantly demonstrated by tables 22 to 25 564 ADOLPH II. SCHULTZ TABLE 22 Aye changes in the percentage frequerrcy of specimens with carious, abscessed, and lost teeth (and average number o f teeth affected in these spechens) in wad higher primates. I n young wild higher primates abscess is pesent only i n one gori2Za (one tooth) and in one chimpanzee (three teeth), whereas caries and loss of teeth are completely lacking. None o f the oaptive higher primates show caries. abscess, and loss of teeth WILD HYLOBATBS -Adult Age Specimens Caries Percentnge of specimens Average number of teeth Abscess Percentage of npeeimens Average number of teeth Closed alveolus Percentage of specimens Average number of teeth 151 1.s 3.0 Adult Old Old Adult Old Adult Old 98.5 1.5 12.5 -- ~ -75 94 48 4.5 21 66 64 1.1 6.7 29.2 4.4 4 . 0 1 . 0 2.7 -- - 2.5 14.6 58.5 2.3 4.1 4.0 18.1 1.0 1.8 I 1.3 2.61.0 ~ -- 18.7 58.3 6.7 61.9 2.0 4.2 8.0 25.0 5.2 5.5 1 1 3.4 1.0 0 fO.5 0 1.s -- 4.8 3.d 9.4 3.0 1.0 3.0 TABLE as Age changes in the percentage frequency of 8pe&ens with carious, abscessed, and lost teeth (and average number of teeth afected in these specimens) in wild ( w . ) and captive (0.) monkeys o f the subfamily Lasiopyginae 1 QENUS Specimens Caries Percentage of specimens Average number of teeth Abscess Percentage of specimens Average numberofteeth W. C. ----C. W. -- LASIOPYQA -- 82 233 0 1.3 0 W. C. PITHECUI 1.3 w. c. w. c. 0 0.4 0 w. c. w. 0 0 0 e. 0 1.o Adult Old 97 31 73 26 21 34 32 4 26 6 2.1 9.7 15.7 23.1 0 0 2.5 2.7 2.0 2.3 0 2.9 0 0 5 .2 9.7 50.1 11.5 4.8 0 6.2 0 50.7 66.7 0 2.6 1.6 1.3 2.5 2.3 5.0 0 1.0 1.6 2.0 1.0 d.1 11.0 11.5 0 53.3 0 0 2.1 2.3 1.0 0 4.2 1.5 0 0 3.0 2.0 Young Adult Adult Old 61 39 84 18 28 4 7.7 553 1.6 0 2.4 16.7 $1.4 50.0 1.0 1.0 1.5 2.7 1.8 3.5 Old -- -- - - - -- - __- 2.0 0 4.5 - 0 0 0 Closed alveolus Percentageof specimens Averagenumberof teeth 0 2.5 0 1 0 0 55.7 25.0 0 1.3 1.2 10.7 5.6 0 5.0 0 0 5.0 -- 565 ERUPTION AND DECAY OF TEETH IN PRIMATES TABLE 24 Age changes in the percentage frequency of specimens with Catiowr, abscessed, and lost teeth (and average number of teeth affected in these specimens) in wild m n k e y s of the subfamily Colobinae. I n dl seventy-nine young Colobinae caries, abscess, and loss of teeth are completely Zucking. The seven captive svecimens examined show no defects in their dentitions ~ COLOBUS WILD Age Adult Specimens Caries Percentage of specimens Averaee number of teeth Abscess Percentage of specimens Averagenumber of teeth Closed alveolus Percentage of specimens Average number of teeth 51 NAEALXS PYOAT- Old Adult Old Adult Old 8 29 12 180 92 0 0 0 0 0 0 0.6 1.1 1.0 2.0 -~--____--- 0 0 I I I i8I I S.9 18.5 5.4 5.6 19.6 1.0 1.0 1.0 1.3 2.0 0 0 TABLE 25 Age changes in the percentage frequency of specimens with cariolls, abscessed, and lost teeth (and average nwnber of teeth affected in these specimens) in wild platyrrhines. None of the y m g platyrrhines have caries, abscess, and loss of teeth. Among the captive p h t p - h i n e s wries is not observed, abscess occurs Q 8 Ateles (adult) (3 teeth), in 1 Cebw (adult) (1 tooth) and 1 Cebw ( O M ) (3 teeth) and loss of teeth in 1 Cebus (adult) ( 5 teeth) WILD Ape I-- ATEUS -I- I Adult Old Adult -- Specimens Caries Percentage of specimens Average number of teeth Abscess Percentage of specimens Average nnmberof teeth Closed alveolus Percentage of specimens Average nnmberof teeth 93 1 CEBUS Old ALOUATTA Adult Old OBDIPOYIDAS -- -- hdult Adult --- Old 63 70 16 132 77 39 a 28 -Z5.0 I I 0 1.S SJ 14.5 2.3 1.7 2.0 -- SJ 38.8 1.7 2.5 1.2 2.0 1.2 2.2 ---- 11.4 5.7 0 7.9 5.7 0 2.2 5.0 u.5 0 s.0 I 1.0 $8.1 I 2.6 10.8 50.0 Old 5 I___ 14.3 $0.0 1.0 - 1.2 2.0 - 1.0 5.1 25.0 S.6 40.0 1.0 2.o 2.0 5.1 19.5 0 1.o - 1.0 0 AYBBICALJ JOUBNAG 01 PEYSICAL ANTHBOPOLOQY, VOL. SIX, NO. 4 1.0 - 0 0 - 566 ADOLPH H. SCHULTZ and, particularly, by the summarizing data in table 27. I t is very evident that, whenever the series of specimens are sufliciently large to give a representative picture, the percentages of specimens with the different pathological conditions increases tremendously from young to adult and from adult to old age. Among the higher primates (table 22) caries is comparatively rare in gorilla, whereas surprisingly frequent in chimpanzee and orang-utan. This is in agreement with the corresponding results of Colyer (’31,p. a), but the percentages of specimens showing caries are very considerably higher, according to the writer’s observations than according to the data by Colyer. The latter discrepancy exists also in regard to most the other primates and calls for some comment which, however, may not offer a complete explanation for these puzzling differences in results. To begin with, Colyer does not subdivide his material according to age, and even slight differences in the age distribution of the specimens examined can change the average incidence of caries very significantly. For instance, in the miter’s series of orang-utans the percentage of specimens with caries amounts to 0 in young animales, to 4.4 in adult ones, and to 28.5 in old ones. The average percentage of the entire series of 95 orang-utans happens to be 8.4,but would differ a great deal with changes in the proportion of young or of old specimens. I n the series of 254 orang-utans examined by Colyer without reference to age caries occurred in 2.4 per cent of the skulls. In a series of 194 other orang-utans, all with completely erupted dentitions, Selenka (1898) found 10 specimens (=5.2 per cent) with caries. There exist still other factors, besides age, which can influence the frequency with which caries is found. In the course of his work in different museums, the writer gained the impression that particularly the older collections, made chiefly for taxonomic purposes, contain comparatively few skulls of really old specimens and few with extensive pathological defects in the dentitions. The suspicion appears, therefore, ERUPTION AND DECAY OF TEETH IN PRIMATES 567 quite justifiable that some field collectors have given preference to ‘normal’ skulls with perfect dentitions and have discarded specimens with symptoms of extreme age or of evident disease. I t must also be taken into consideration that many field workers collect usually “one large male and one typical female” from each locality, i.e., only two individuals out of an entire local population. With the uneven representation of the different ages within a group of primates (as well as for certain other causes, as differing degrees of curiosity, speed, aggressiveness, etc.) adult specimens are secured in nearly all instances, whereas old ones only in exceptional cases. These may be the reasons, why, for instance, 15 of the 19 skulls of wild chimpanzees, showing caries, are in the Hamann Museum of Anatomy and Comparative Anthropology, in which detailed taxonomic problems play but a minor role, whereas only 4 chimpanzees with caries could be found in all the other collections visited by the author. In other words, caries among adult or old chimpanzees exists in 20.3 per cent of the specimens in the Hamann Museum, whereas in only 7.5 per cent of all the other adult and old chimpanzee material examined. For probably the same reasons the taxonomic collections of the U. S. National Museum and Biological Survey contain, e.g., among their material of 43 wild, adult and old capuchins only 2.3 per cent of specimens with abscess formation and among 49 wild, adult and old spider monkeys only 6.1 per cent of cases showing abscess. In the corresponding series of the author’s collection these percentages are much higher, namely, 11.9 for 42 capuchins and 16.8 for 107 spider monkeys. This material had been collected in the field by the writer, who had carefully saved every skull, regardless of age or of any pathological conditions, endeavoring to secure really representative samples of entire monkey populations. Besides age and the possibility of selection of material according to the chief aim of some collections, there exists in all likelihood a third factor which can influence the frequency of the occurrence of caries, etc. This factor is in a 568 ADOLPH H. SCHULTZ sense a geographical one and is best indicated by the following example: Of 11 specimens of Ateles geoffroyi from the jungle near Talamanca, Costa Rica, 4 show caries on the crowns of the lower M1 and M2. In this locality, therefore, caries occurs among spider monkeys in 36.4 per cent of the cases. Among the other 145 wild adult and old spider monkeys from different localities (but including a majority of specimens of the same species, A. geoffroyi) caries is present in only 5.5 per cent of the cases. This su5ices to show that local varieties of a species may in some instances manifest a predisposition or at least a special susceptibility for caries. That some types of primates possess a striking resistance to carious infections is clearly demonstrated by the data in table 26 (compare also tables 23, 24 and 25). Caries in the subfamily Colobinae occurs in only 0.4 per cent (only 2 langurs) of the entire material, whereas in the closely allied subfamily Lasiopyginae this percentage amounts to 4.6. Among platyrrhines there exists an even more marked difference in this respect, since caries is found in only 0.3 per cent of howlers (only 1 of 282 specimens), but in 9.0 per cent of all other New World monkeys12 examined. The general percentage frequencies of abscesses and of closed alveoli do not differ anywhere near as much in the various groups of primates, but the data in table 26 show convincingly that abscess and closed alveolus are in general more common in the higher than in the lower primates. Table 27 demonstrates the fact that captivity influences very markedly the frequency of cariesfs in all age groups, but changes the frequency of abscess very little1* and that of 'According to Colyer ( '31, p. 44), not only Alouatta, but also the platyrrhine genera Aotaa, Callicebus, Cacajao and Brachyteles (not examined by the d t e r ) are free from caries in the wild and captive states. 'A much greater frequency of caries in captive than in wild monkeys baa also been found by Turner ( '14) and by Colyer ( '31). Incidentally, the former author states that caries is found in 5.3 per cent of the skulls of wild monkeys in the British Museum. %Judgingby the small series of old captive specimens, absceases are considerably less frequent during old age in captive than in wild monkeys. 569 ERUPTION AND DECAY OF TEETH IN PBIMATES closed alveoli not at all. The greater frequency of caries in captive than in wild primates can probably be traced back to inadequate diet in the state of captivity, affecting particularly animals captured young. Dietary insdciencies, however, will not explain the much more striking differences in the TABLE 26 Percentages of specimens with caries, abscess, and closed alveolus in different grovps of primates (all ages oombined, but considering only d i d specirnene) I I WILD PBIMATLS or u AQLS 1 SPLCIYZNS Large apes and gibbons Rubfamily Lasiopyginae Subfamily Colobinae Platyrrhineswithout Alouatta Geuas Alouatta I PLBCLNTAO= or spmmmxsw Cariea I AbLbacesa rm Cloned dvaolns 744 504 451 5.2 4.6 0.4 20.2 9.5 7.1 6.7 4.6 2.2 413 282 9.0 0.3 8.2 2.9 3.5 7.4 TABLE 27 Age changes in the percentages of specimens showing wries, abscess, or closed alveolw on one or more teeth in wild and in captive primates (all genera combined) I I WILD SPLOIYLNS C-IPLOIXENS AQL Total of specimens Caries Abscess Closed alveolus Young Adult 587 1172 635 0.2 0.5 0 2.9 6.3 2.6 10.5 32.9 11.7 Old -~ 1.0 0.5 0 24.4 21.9 12.2 incidence of caries between certain groups of wild primates. Thus, the writer has shot howlers and capuchins in the same trees, where they had been eating the same food, as shown by their stomach contents, yet caries is found in 25 per cent of old capuchins, whereas in only 1.3 per cent of old howlers. I t has been shown above that the dentitions of certain types of primates are much more susceptible to partial destruction by caries than are the dentitions of other types. It will now 570 ADOLPH H. SCHULTZ be demonstrated that certain teeth are much more likely to have carious cavities than are other teeth. This is evident, first of all, from the following finding: Of the total of 261 teeth with caries only 115 teeth, or 44 per cent, are asymmetrical in distribution within the same dentition, whereas 56 per cent of these teeth are corresponding teeth on both sides of the same jaw. If caries were to affect the 32 or 36 teeth of a dentition indiscriminately, one would never encounter 73 pairs of right and left teeth in this series of 122 specimens showing caries, and this on an average in only 2.1 teeth per specimen. Since in over half the cases with caries the same tooth is affected in the right as in the left half of the jaw, it is certain that the different types of teeth possess widely varying degrees of constitutional resistance to caries.I6 This conclusion is also supported by the data presented in figure 21. According to the diagrams showing the percentage distribution of caries among the different teeth, the I1 and the M1 bear the relatively highest numbers of carious cavities. I n wild catarrhines caries is found on Incisors in 50 per cent of all affected teeth and on M1 in 16 per cent; in captive catarrhines the Incisors show caries in only 34 per cent, but the M1 in 38 per cent of the cases. Judging by the corresponding data of Colyer (’31, p. 44), this difference between wild and captive catarrhines is even more pronounced in his extensive material. According to the latter author as well as according to the writer’s results, caries in platyrrhines exists chiefly in the Incisors and Molars, cavities in the other teeth occurring in only 9 per cent of all cases of caries according to Colyer and in only 25 per cent according to the author. I n both, catarrhines and platyrrhines caries is somewhat more frequent in the upper than in the lower jaw. “Of the total of 770 teeth with abscesses 61 per cent are asymmetrically distributed within single dentit.ions, and only the remaining 39 per cent show aymmetncd disposition, affecting corresponding teeth in the right and the left half of a jaw. It must also be considered that the average number of abscesses per specimen with this condition amounts to 2.6, i.e., to more than the corresponding average for caries; the higher this average the greater the probability for symmetrical distribution by chance alone. ERUPTION AND DECAY OF TEETH I N PRIMATES 571 As shown by the lower left diagrams in figure 21, there exists comparatively little discrimination among the different teeth in regard to abscess, except that the Canines of platyrrhines have alveolar abscesses with astonishing frequency. Abscesses on Canines may be connected with fighting among males, causing fractures of their large Canines or of the corresponding alveoli. In Alouatta, e.g., abscesses on Canines I I Fig.21 Percentage frequencies with which caries, abscess, and closure of alveolus are found in the different teeth. The distribution of the incidence of caries among the various teeth is shown in the upper half of the picture, for catarrhines and for platyrrhinee in the two diagrams on the left, for wild and for captive catarrhines in the two diagrams on the right. The d i a g r a m a in the lower half of the figure show the distribution among the various teeth of abscesses (on the left) and of closed alveoli (on the right). 572 ADOLPH H. SCHULTZ are recorded for 15 out of 95 adult or old males (=15.8 per cent), but for only 3 out of 115 females (= 2.6 per cent). In some catarrhine genera abscesses on the Canines of males are even more frequent than in the just mentioned example of platyrrhines. Thus, in adult or old gorillas this condition exists in only 6 out of 88 females (=6.8 per cent), but in 35 out of 157 males (= 22.3 per cent). The excessive enlargement of the Canines in males of some primates has evidently its decided disadvantages, since it is very apt to concur sooner or later with a developing abscess. I n Old World as well as in New World primates abscesses, just as carious cavities, are more frequent on the M1 than on the M2 and more frequent on the latter than on the M3. Abscess formation, just as caries, is on an average somewhat more common in the upper than in the lower jaw. As shown by the diagrams in the lower right quarter of figure 21, closed alveoli are more common for Incisors, particularly 12, than for any other teeth. In catarrhines the premature loss of teeth becomes, in general, less and less frequent from the Incisors to the last Molars. This does not correspond to the relative frequency of caries and abscess in the different teeth, nor to the progress of attrition. This unexplained lack of correlation between the loss of teeth and the pathological hdings on teeth is clearly shown by the following example: In catarrhines the alveoli of the I2 are closed in 28 per cent of all cases of closed alveoli, whereas the alveoli of the M1 are closed in only 7 per cent of all cases. On the other hand, caries affects the I2 in only 11 per cent of all cases of caries, whereas the M1 in 23 per cent of the cases, and abscess is found on the I2 in 9 per cent of all cases of abscess, but on the M1 in 20 per cent. In other words, caries and abscess occur on the I2 less than one-half as often as on the M1, but the 12 are lost and their alveoli are closed four times more frequently than the M1. It remains to compare briefly some of the data on dental pathology in apes and monkeys with the corresponding con$tions in man, particularly the lower human races. These ERUPTION AND DECAY OF TEETH I N PRIMATES 573 comparisons have to be restricted to a few examples, chosen at random from the mass of available data appertaining to the frequency and distribution of caries, etc., in man. Pickerill ( ’23) has collected some convenient statistics showing the incidence of carious dentitions in different racial and other groups of man. These percentages range between 1.4 (Eskimos) and 20.8 (Negroes) among the colored races and amount to anywhere from 86 to 99 in different groups of modern whites. A comparison with table 26 shows clearly that specimens with caries are more common in many groups of monkeys and apes than in some few human races. The percentage of carious teeth, however, is probably always higher in modern man than in other primates. In full grown wild gibbons and large apes there are on an average only 0.6 per cent of all teeth carious, in full grown wild lower catarrhines this percentage amounts to only 0.2, and in full grown wild platyrrhines to 0.3. According to Pickerill, the percentages of carious teeth vary in ‘uncivilized races’ between 2 and 7 and in ‘highly civilized races’ between 15 and 52. In Seminole Indians, Hamlin (’33) finds 29.7 per cent of all teeth to be carious, whereas for Bantus, Shaw (’31) obtains a corresponding percentage of only 1.85. Age iduences the frequency of caries very profoundly not only in apes and monkeys, but also in man. For instance, among boys of Prague carious permanent teeth were found in 25 per cent of individuals 8 years old, in 74 per cent of individuals 12 years old, and in 90 per cent of individuals 19 years old; in relation to the total number of permanent teeth the cases of carious teeth amount to (upper jaw) 3.5 per cent at 8 years, 7 per cent at 12 years, and 25 per cent at 19 years (Sub, ’19). Again as in other primates, caries in man affects corresponding teeth on the right and the left side of a jaw much more frequently than different forms of teeth in the same dentition. Thus, Suk (’19) has reported that of 1764 carious teethsin Prague children 546 (belonging to 152 individuals) were asymmetrically distributed, whereas 1218 decayed teeth (of 364 individuals) were found in couples, i.e., symmetrically disposed on the right and left sides of a jaw. A Y P B I C A N JOURNAL OF PHYSICAL ANTHROPOLOGY, VOL. XlS, NO. 4 574 ADOLPH H. SCHULTZ The somewhat greater frequency of caries in the upper than in the lower jaw of monkeys and apes is also in agreement with this relation in man, according to the majority of observers. It has been shown that caries in apes and monkeys affects, in general, most frequently the M1 and the upper 11. Different human races differ apparently a good deal in regard to this relative susceptibility to caries of various teeth. For instance, in children of Prague and in young Zulus caries is found on the M1 with the highest and on the M2 with the second highest frequency, but on the I1 and I2 caries is rare (Suk, '19). The same relation exists in adult Bantus (Shaw, '31) and in skulls of predynastic Egyptians (Ruffer, '20). In Seminole Indians caries affects the different teeth with comparatively little discrimination and occurs quite frequently on the upper Incisors (Hamlin, '33). In other Indians HrdliEka ( ' 0 8 ) found caries most commonly on the Premolars and Molars. I n the ancient inhabitants of Guam the M2 are carious much more frequently than any of the other teeth (Leigh, '30). It must sdlice here to state the general conclusion that the frequency of the various forms of 'alveolar abscess' in, particularly old, apes is a t least as great as the general average frequency of these conditions in modern man, though different human races vary a great deal in this respect. That dental abscesses, due to a variety of causes, were already very common in ancient human populations has been clearly demonstrated by many investigators, e.g., Ruffer ( '20), MacCurdy ( '23), Chappel ( '27), and Moodie ( '31). I n regard to ante-mortem loss of teeth, there exists a very striking difference between apes and monkeys on one side and man on the other. In the latter the M3 are, as a rule, lost much more frequently than any of the other teeth, as shown, for instance, by Leigh ('30) for the ancient population of Guam and by Stewart ('31) for the pre-Columbian Peruvians. I n sharp contrast to this, the M3 of apes and monkeys are more rarely lost before death than the other teeth. ERUPTION AND DECAY OF TEETH IN PRIMATES 575 SUMMARY This paper represents chiefly a collection of information on some relations between age and dentition in monkeys and apes and thus it furnishes comparative data, needed in the interpretation of age changes in the dentition of man. The available information is in part still very fragmentary and as yet far from permitting many general conclusions. For this reason only the more adequately supported results will be listed in the following brief enumeration of findings. The deciduous dentition erupts at earlier ages in macaques and gibbons than in the large apes and at much earlier ages in all apes than in man. The tentative, average age of eruption of the permanent dentition reaches in the macaque from the second half of the second to (probably at most) the middle of the eighth year, in the chimpanzee from the end of the third to the end of the tenth year, and in man from the beginning of the seventh to the end of the nineteenth year. In all these primates the ages at which the various teeth appear fluctuate individually to a very considerable extent. Not only in man, but also in the chimpanzee and in the macaque there exists a relatively long resting period before the eruption of the last Molars. In all primates examined, except man, the eruption of the first Molars is followed by a comparatively long intermission before further teeth are being added to the permanent dentition. The detailed survey of the sequence of eruption of the permanent teeth in monkeys and apes is based chiefly upon observations on large series of skulls of which a total of 2908 specimens has been examined. The permanent dentition starts in all p r i w t e s with the eruption of the lower M1, followed by that of the upper M1, except in man in whom the lower I1 can frequently be the second permanent teeth. In squirrel monkeys and langurs the M2 appear after all the M1, whereas in the other primates examined the I1 erupt as the second form of permanent teeth. In gnerezas the M2 appear, as a rule, before the 12, but in the great majority 576 ADOLPH E. SCHTJLTZ of monkeys and apes this relation is reversed, the I 2 following immediately after the I1 and the lower I2 preceding the upper 12. In all primates, except man, the Premolars erupt in rapid and varying succession after the M2 have been added to the dentition, but before the Canines make their appearance. The lower M3 and subsequently the upper M3 are thc last teeth to erupt in all primates, with the exception of langurs (and lower jaw of squirrel monkeys) in which the M3 appear before the Premolars and Canines. This early addition of the last Molars is probably to be regarded as a primitive condition and occurs in the same monkeys which are distinguished by an exceptionally early eruption of the M2. The sequence of eruption of the permanent dentition of modern man has become much more specialized than that of any other primate. These extreme changes consist in the eruption of the Incisors following generally without any resting period that of the M1, in the eruption of the Premolars and Canines before that of the M2, and in the frequent appearance of the lower C before the eruption of the P2. Two specimens of Neanderthal man of suitable dental development still show the less specialized, simian condition of the eruption of M2 before the appearance of all Premolars. I n many primates, including man, the Canines of males erupt slightly later and often more slowly than those of females. With comparatively few exceptions, the teeth of the lower jaw erupt before the corresponding teeth of the upper jaw, this difference being most regular and pronounced in regard to the Molars. The review of the scattered and frequently conflicting statements by other authors regarding the sequence of eruption of the teeth in.primates reveals the fact that the many erroneous conclusions in the literature are mostly based upon entirely inadequate series of observations. Noteworthy attrition of the permanent .teeth is very rare before the completion of the dentition. Marked attrition appears first on the M1, the Inoisors and, less regularly, on ERUPTION AND DECAY OF TEETH I N PRIMATES 577 the Canines. The M2 become worn after the just mentioned teeth, but usually before the Premolars. The M3 are generally the last teeth to become affected by advanced attrition. Among old specimens the Incisors and Canines are more frequently worn to the gums than any other teeth. Extreme attrition is most common among the higher primates and least frequent among the platyrrhines (except Ateles). The base suture and the sagittal suture are with very few individual exceptions open during the entire period of dental eruption. After the closure of both these sutures marked attrition of the teeth becomes, in general, much more common than among skulls with one or both sutures still open. The numerous correlations between suture closure and dental attrition in the different primate genera are shown more clearly and briefly in table 20 than they could be summarized here. Deviations from the normal conditions of the permanent dentition are found with varying and at times surprisingly high frequencies in all the major groups of primates examined. Striking reductions in the size of teeth occur chiefly in the M3. Such vestigial M3 are particularly frequent in gibbons and among the platyrrhine spider monkeys, capuchins, and squirrel monkeys. Among the same primates, except the last named group, the .complete elimination of M3 is also much more common than in the other genera. Fourth Molars are found chiefly among the large apes. The congenital lack of Incisors and of Premolars occurs in rare instances among a wide variety of monkeys and apes. Marked crowding of teeth is much more common in the case of Incisors and Premolars than in the case of other teeth and is more frequent in the upper than in the lower jaw. Crowding of Incisors is most commonly met with in langurs, whereas displacement of Premolars is most frequent in chimpanzees and in howlers. Impacted teeth have been observed in 24 specimens of which 12 are anthropoids. Abnormally long retained deciduous teeth are present in 1& fully adult primates, belonging to seven different genera. 578 ADOLPH 11. SCHULTZ Caries and alveolar abscesses are extremely rare on the deciduous teeth of monkeys and apes. On the permanent dentition these pathological conditions become very much more frequent in adult than in young and in old than in adult specimens. Carious teeth are rare in gorillas, but comparatively frequent in chimpanzees and orang-utans. Similar, wide differences in regard to the frequency of caries exist in other groups of primates. Thus, caries is very rare in Colobinae, whereas quite common in Lasiopyginae, and it is extremely rare in howlers, but comparatively frequent in other platyrrhines. The frequencies of abscess and of loss of teeth do not M e r nearly as much in different types of primates as does the incidence of caries. In over half the dentitions with caries the cavities occur in the same teeth on the right and the left side of a: jaw. Caries affects the I1 and the M1 much more frequently than any of the other teeth and it is found somewhat more commonly in the upper than in the lower jaw. Abscesses are much less unevenly distributed among the different teeth, except that they are found in an exceptionally high percentage of cases on the Canines of (male) platyrrhines. The I 2 of monkeys and apes become prematurely lost in a higher proportion of cases than any of the other teeth; the I1 stand second in this respect and the M3 last. By means of preliminary comparisons, it is shown that the pathological conditions of the dentition of man are in many respects very similar to, in other respects quite different from, the corresponding conditions in apes and monkeys. The combined data on advanced attrition of teeth and on the gradual pathological destruction and loss of teeth and of alveolar walls reveal a surprising prevalence of these conditions in simian primates of old age. The dentition begins to break down before the termination of the normal life span not only in man, but in apes and monkeys as well. 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