Morphology of the Cerebellar Dentate Nucleus in a Chimpanzee GARMAN HARLOW DARON T h e University of O k l a h o m a Medical Center, O k l a h o m a City, O k l a h o m a Recent contributions to our knowledge in the field of neurophysiology of the cerebellum have stimulated additional morphological studies. Evidence suggesting that the cerebellar nuclei function in more than a simple relay capacity draws added attention to their structure. The large size of the dentate nucleus in man with its thin lamina, discrete borders and extensive convolutions must be associated with unique features of cerebellar function. This specific organization of the dentate nucleus is a characteristic feature in the anthropoid apes and man. In some of the subprimates the dentate nucleus shows a tendency toward lamination and folding. However, the lamina is wide with rather poorly defined borders and the outer contour exhibits only broad, gentle undulations. A shallow hilar region may be present. In lower primates, e.g., the macaque monkey, the dentate nucleus also has a simple form. Wax model reconstructions of the cerebellar nuclei of the macaque exhibit a definite hilus in the dentate nucleus opening ventromedially and superiorly. The outer contour is smoothly curved with one broad, shallow sulcus on the dorsolateral surface near the inferior extremity of the nucleus. The emboliform nucleus is rather broadly continuous with the inferior portion of the dentate nucleus. The gray lamina is broad and irregular in thickness. In the gibbon (Tilney, ' 2 8 ) the dentate nucleus shows more of the features characteristic of its configuration in the higher primates. The nucleus has a number of well-defined plications especially along the lateral wall. In the latter region the lamina is thinner and the borders are more distinct than elsewhere. The dentate nucleus in the orangutan, chimpanzee and gorilla exhibit a marked difference from that in the lower species and great similarity to the human nucleus. Tilney ('28) presents photographs of stained sections through the dentate nucleus in these three species. The appearance of this nucleus in sections, especially in the chimpanzee and gorilla is remarkably like that in the human. The lamina is thin with well defined borders, extensively folded into furrows and ridges over the entire nucleus. A well defined hilus is visible in appropriate sections. The great similarity of the dentate nucleus in the higher primates and man indicate that studies of these anthropoid species would aid in the understanding of this nucleus in man. There is a paucity of morphological data on the primate cerebellar nuclei. The value of quantitative data in neuroanatomical investigations is becoming more apparent. These factors led to this study of the morphology and volume determination of the dentate nuclear in a chimpanzee specimen that we obtained. MATERIAL AND METHOD The study is based upon a specimen obtained through the courtesy of the Oklahoma City Zoo. This adult, female animal had been in the zoo for several years and becoming somewhat vicious, was killed. The exact weight and age are unknown. The brain was removed a few hours after death and submerged, intact, in 10% formalin. Eleven months later the brain weighed 349 gm and had these measurements: greatest width, 91 mm; frontal to occipital poles, 106 mm; basal surface of temporal lobe to vertex, 61 mm. No abnormalities were noted then or in subsequent studies. The infratentorial brain stem, including the cerebellum, was removed by a transverse cut at the level of the inferior colliculus. The cerebellar cortex and underlying white matter was cut away as ex81 82 GARMAN HARLOW DARON tensively as possible without cutting into are those customarily used in describing the cerebellar nuclei. This reduced block the infratentorial brain stem. Thus, for of brain stem was then embedded in paraf- the cerebellar nuclei the terms dorsal-venfin using the ethyl alcohol-xylol technique. tral and superior-inferior denote axial lines The block of tissue was cut into serial sec- parallel with these same axes as applied tions at 15 in a transverse plane at right to the medulla and pons. The superior-inangles with the longitudinal axis of the ferior axis through the cerebellar nuclei will be considered as a line parallel with infr atentorial brain stem. For this study every fifth section the floor of the fourth ventricle. A section throughout the extent of the cerebellar cut in a plane at right angles to the supenuclei was stained using the luxol fast rior-inferior axis is a transverse section of blue-cresyl violet procedure (Kluver and the cerebellar nuclei. A section cut in a Barrera, ’53). Photographs were made of plane at right angles to the dorsal-ventral every tenth section at a magnification of axis will be considered as a frontal section of these nuclei (discussion on p. 89). 18 diameters. Configuration. The following descripA wax plate model of the right dentate nucleus was reconstructed from the photo- tion is based upon study of both the wax graphs utilizing midsagittal structures and model reconstruction and the stained serial the floor of the fourth ventricle as guide sections. The substantia grisea of which the dentate nucleus is composed is arplanes for orientation. The volume of the dentate nucleus was ranged in a thin lamina which is disposed determined in the following manner. First, in rather definitely patterned gyral-like the limiting boundary of the nuclear mate- folds. Furthermore, this folded lamina is rial as seen in the photographs was care- grossly fashioned as the cortex of an irfully outlined with the aid of microscopic regular, incomplete spheroid. Thus, the reference to the stained sections. The area dentate nucleus has external and internal occupied by the nuclear material, so out- surfaces. These surfaces become continlined, was measured with a planimeter. uous at the lip-like border of a hilar region. Five readings were made of each section The white matter which occupies the inand the average value determined. The terior of this spheroid is continuous area measurements of each section were through the hilus with the general white then plotted to scale on a line graph and matter of the corpus medullare and in no the volume determined by the method of gross respect differs from it. planimetric measurement of the “area unThe dentate nucleus is considerably flatder the graph.” Since these measurements tened along a dorsolateral-ventromedial and graph plotting were done at a magni- axis. Due to the position of the hilus this fication of 18 the volume reading was re- flattening is more pronounced dorsally so duced by 183to natural size value. three surfaces can be described, viz., dorThe average width of the lamina of gray solateral, ventral and ventromedial (fig. matter comprising the nucleus was deter- 5). Correspondingly, three borders exist; mined from the stained sections by using a dorsomedial, ventrolateral and ventromedcalibrated ocular micrometer. This infor- ial. These surfaces and borders converge mation together with the volume made pos- dorsoinferiorly to produce an inferior pole. sible an estimation of the surface area. There is only a slight degree of tapering superiorly so the nucleus also exhibits a MORPHOLOGICAL FINDINGS superior border (figs. 1, 2). Planes and axes of reference. The folThe large hilar orifice opens onto the lowing statements are necessitated by vari- superior and dorsal half of the ventromedations found in the literature in regard to ial surfaces (figs. 2, 3 ) . This opening is the nomenclature of planes and axes of somewhat triangular in shape so that its reference pertaining to the cerebellar nu- borders constitute superior, dorsal and clei. Since the cerebellar nuclei lie in the ventral lips (fig. 4 ) . The superior lip, corpus medullare of the cerebellum dorsal which is also the superior border of the and dorsolateral to the fourth ventricle, nucleus, is somewhat J-shaped as viewed the most satisfactory positional references from the superior aspect on the left side DENTATE NUCLEUS I N A CHIMPANZEE or as a reversed J on the right side. The long arm of the J is the superior border of the dorsolateral surface while the curved portion is the same border of the ventral and ventromedial surfaces of the nucleus (fig. 3 ) . The dorsal lip of the hilus presents a very distinct, straight line extending inferiorly from the dorsal limit of the superior lip nearly to the inferior pole. This line is approximately parallel with both the sagittal axis and the floor of the fourth ventricle. The ventral lip of the hilus presents a jagged line extending obliquely from the ventromedial limit of the superior lip nearly to the inferior pole (figs. 2, 3, 4). These three lips (viz., superior, dorsal and ventral) circumscribe the hilar region and are roughly disposed as the sides of a right triangle with the ventral lip forming the hypotenuse. 83 The dorsolateral surface of the dentate nucleus is bounded by the dorsomedial, superior and ventrolateral borders (fig. 1 ). The dorsomedial border coincides with the dorsal lip of the hilus in the superior two thirds of the nucleus (fig. 4). The superior border is rather straight and nearly parallel with the dorsal-ventral axis. The ventrolateral border forms an arched line from the ventrolateral portion of the superior border to the dorsally placed inferior pole. The greatest width of the dorsolateral surface is about one-fourth of the length of the nucleus from the superior border (fig. 1). The most characteristc feature of the dorsolateral surf ace is the orderly arrangement of gyri. The gyri consist of relatively straight, continuous, parallel longitudinal ridges extending inferiorly from the superior border. In the inferior and lateral por- Fig. 1 Photograph of a wax model reconstruction of the right dentate nucleus in the chimpanzee. Dorsolateral surface. See figure 5A for aspect of orientation. 84 GARMAN HARLOW DARON Fig. 2 Photograph of the ventromedial aspect of the same model as shown in figure 1. See figure 5A for aspect of orientation. A, B, C, levels of transverse sections shown in figure 5. tion of the dorsolateral surface there is a slight ventral deviation of the gyri. The dorsally placed gyri are considerably narrower than those in the ventral portion. Furthermore, the gyri, particularly the more ventral ones, are narrower superiorly becoming broader as they extend inferiorly. It follows, that the dorsal and superior portion may be designated as a microgyric area as will be discussed later. Correspondingly, the more ventral and inferior portion may be called the macrogyric area. However, it is apparent from the model and sections that the transition is gradual and no sharp line of demarcation between these areas is indicated. On this surface there are a few deep sulci with several shallow ones intervening. The latter are especially numerous in the dorsomedial portion of the nucleus. The ventral surface of the dentate nucleus is considerably smaller than the dorsolateral surface. Superiorly it is broad and rather sharply demarcated by ventrolateral and ventromedial borders from the dorsolateral and ventromedial surf aces respectively (fig. 5 A ) . Inferiorly the ventral surface is much narrower and rounded so that these limiting borders are very indistinct (fig. 5C). Thus, in the inferior half of the nucleus the ventral surface merely constitutes a rounded area of continuity from the dorsolateral to the ventromedial surfaces. The gyral pattern on this surface will be described later. The ventromedial aspect of the dentate nucleus (fig. 2 ) presents the same contour and limiting borders as the dorsolateral, viz., relatively straight dorsomedial and superior borders and a curve semicircular DENTATE NUCLEUS IN A CHIMPANZEE Fig. 3 85 Superior-medial aspect of the same model as shown in figure 1. ventral border. This area is divided into two, approximately equal subdivisions. First, a large superior and dorsal right triangular area which constitutes the hilar orifice and which has already been described. Second, a ventral and inferior region which makes up the medial portion of the nucleus. Within the hilar area, as can be seen on the model, is presented the inner surface of the dorsolateral portion of the nucleus. This exhibits a gyral and sulcal pattern which is the reciprocal of that seen on the dorsolateral aspect. Ventral to the ventral hilar lip the concavity of the nucleus presents a ventrolateral and inferior recess (fig. 3 ) . The medial portion of the nucleus is bounded dorsally by the jagged, diagonally directed, ventral lip of the hilar orifice. This portion of the nucleus is continued ventrolaterally from the ventral lip to the ventromedial border where it becomes continuous with the ventral surface. The gyri on the ventral and ventromedial surfaces are, for the most part, continuations of the gyri on the dorsolateral surface. The more dorsal gyri on the latter surface are continuous around the inferior pole onto the ventromedial surface u p to the ventral hilar lip. The ventral deviation of the larger, ventral gyri on the dorsolateral surface as they are followed inferiorly, represent the beginning of a long spiral pattern as these gyri extend onto the ventral and ventromedial surfaces. This is more readily noted if the sulcal pattern is followed. On the ventromedial surface these gyri become largely effaced by flattening. The sulci thus be- 86 G A R M A N H A R L O W DARON ,,.. .....- .._. * Fig. 4 Outline drawing of figure 2. Ventromedial aspect of right dentate nucleus showing boundaries of the hilus. Emb.. aortion of the emboliform nucleus that is continuous, in transverse sections, with the dentate nucleus. Dotted line marks site of continuity of emboliform and dentate nuclei. come less marked and come closer together in the inferior half of the ventral hilar lip (fig. 2 ) . Orientation with reference to brain stem axes. The dorsomedial border of the dentate nucleus is a rather stable landmark for orientation. It is approximately a straight line and maintains, from its superior to inferior extent, a fairly constant distance of 5.5 mm from the midsagittal plane. This border also maintains a fairly constant relation to the floor of the fourth ventricle, there being only a slight dorsal deviation in this plane from superior to inferior. In the central region this dorsomedial border is about 8.5 mm dorsal to the level of the floor of the ventricle. The dorsolateral surface is slightly convex dorsolaterally but in general lies in a plane which forms an angle of approximately 30" with the transverse axis (fig. 5). This surface deviates slightly laterally from its superior toward its inferior extent. The orientation of the ventromedial surface is difficult to define due to the large hilar area and a marked lateral deviation from superior to inferior. However, a favorable view of this surface of the nucleus was taken from an aspect of about 20" ventral from the transverse axis (figs. 2, 5). Continuity o f the dentate and ernboliform nuclei. The emboliform nucleus is a flat lamina of gray matter disposed roughly in a parasagittal plane, its dorsal margin being somewhat medial to its ventral margin. This nucleus occupies a portion of the hilar region. It is separated from the dentate nucleus except for its most inferior portion. The dorsal margin of the emboliform nucleus is parallel and in close relationship with the dorsomedial border of the dentate nucleus (fig. 5B). On the inferior one-third of the dentate nucleus the dorsomedial border presents a short hook-like extension ventralward (figs. 5B, 2, 3 ) . Thus, in this region the dorsal lip of the hilus does not exactly coincide with the dorsomedial border of the nu- DENTATE NUCLEUG IN A CHIMPANZEE 87 Ventromedid Surface A Fig. 5 Outline drawings of transverse sections of the dentate nucleus at levels marked A, B and C on figure 2. E, emboliform nucleus; J, site of junction of emboliform and dentate nuclei. cleus. In the inferior one-fourth of the nucleus the free edge of this hook-like process is fused with the dorsal margin of the emboliform nucleus. The site and extent of this continuity is indicated by the dotted line on figure 4. Only this attached portion of the emboliform nucleus was included in the wax model. The ventral margin of the reconstructed portion of the emboliform nucleus is separated from the ventral hilar Lip by a narrow slit (0.2 mm). This relationship is maintained inferiorly. Since the inferior lip extends dorsoinferiorly, the emboliform nucleus in this region, and 88 GARMAN HARLOW DARON from this aspect, is triangular in shape with an apex near the inferior pole. The fusion of this inferior triangular portion of the emboliform with the dentate nucleus is so complete that decision on a site of junction is quite arbitrary. An attempt to identify a sharp line of junction between these nuclei on the basis of neuronal cell types and cell distribution was unsuccessful. Thus, these two nuclei are fused in a histologically continuous manner and the described line of fusion is made solely on a gross topographical basis. Linear dimensions. The following dimensions were determined from the wax model but given here as converted to natural size. Measurements made along various axes are given in table 1. The superior-inferior extent is 10.7 mm. The width and height as measured along lines parallel to the transverse and dorsal-ventral axes of the brain stem are 8.3 and 7.2 mm, respectively. A better concept of the size of the nucleus is gained from measurements made along axes intrinsic to the dentate nucleus. Here the superior-inferior extent is as given above since the longitudinal axis of the nucleus is almost exactly in the longitudinal axis of the brain stem. The distance from the dorsomedial to the ventrolateral borders of the nucleus at their greatest separation is 9.4 mm. What may be designated as the width of the nucleus, i.e., from the ventromedial to the dorsolateral surface, varies considerably. At level A in figure 2, where this dimension is greatest, it is 6.4 mm, while at level C in the same figure it is 3.3 mm. Linear dimensions of the hilar orifice as measured along straight lines are as follows: from the dorsal lip to the ventral lip at the superior border, 6.0 mm; from the superior border to the inferior extent of the hilus along the dorsal lip, 8.5 mm; from the superior border to the inferior extent of the hilus along the ventral lip, 10.5 mm. Thickness of the dentate nuclear lamina. Measurements were made of the thickness of the dentate nuclear lamina on the stained sections with a calibrated ocular micrometer. Certain factors effect the accuracy of the measurements. First, under microscopic examination it is difficult to define a sharp line of junction between the nucleus and the surrounding white matter. Also, the type and differentiation of the stain effect the definition of this border. The undulating contour of the dentate nucleus allows for a great deal of tangential sectioning. Natural variations in the thickness of the lamina appear to occur. Upon consideration of these factors sample regions were carefully selected and the thickness measured. The average of 65 measurements is 0.16 mm, with a range from 0.11 to 0.20 mm. Volume. The procedure for determining the volume of the gray matter constituting this nucleus is given on page 82. The value obtained is 84.76 mm3. It is to be noted that this is the volume of the nuclear gray matter and does not include the white matter which occupies the concavity of the dentate field. Surface area. Since the thickness of the dentate lamina is fairly uniform over the entire nucleus both on the surface of the gyri and in the sulci it appears that a reasonable value for the outer surface area is the quotient of the volume divided by the thickness of the nuclear lamina. This results in a value of 547 mma. Due to the large relative size of the dentate nucleus TABLE 1 Comparison of Zineat measurements of the dentate nucleus Chimpanzee Human newborn (Fowler, '01 ) Human adult (Jakob, '28 ) mm mm mm 10.7 8.3 7.2 9.8 - 16-21 - 7-11 9.4 9.7 3.9 - ~~ In superior-inferioraxis In transverse axis of brain stem In dorsal-ventral axis of brain stem Dorsomedial to ventrolateral borders; greatest extent Dorsolateral to ventromedial surf aces 3.3-6.4 8 DENTATE NUCLEUS IN A CHIMPANZEE in contrast to the thickness of the lamina the inner surface must have approximately the same area. DISCUSSION Planes and axes o f reference. In comparing the topography of cerebellar nuclei of various specimens or species solely from microscopic sections, it is important that the exact planes and axes of reference be understood. Confusion exists particularly with reference to man and other primates where the longitudinal axis of the infratentorial brain stem deviates markedly from the cerebral fronto-occipital axis. Published figures illustrate that sections of cerebellar nuclei have been made, named and described without making clear two differing positional points of reference. First, the cerebellar nuclei may be oriented and sectioned with respect to the longitudinal axis of the infratentorial brain stem. Here the terms of transverse and frontal (or horizontal) are readily understood as being at right angles with each other. Other figures have been described where the nuclei have been sectioned in conjunction with the entire brain. In these circumstances the orientation of the plane of sectioning is described with reference to the axes of the cerebrum. Here, sections made in a plane at right angles to the cerebral fronto-occipital axis are designated as transverse or frontal. In this case, when serial sectioning is continued occipitalward the cerebellum and brain stem are sectioned in an oblique fashion. Consequently, in such sections through the dentate nucleus, what is frequently described as dorsal and ventral is more accurately, dorso-superior and ventro-inferior. Thus, in descriptions of the cerebellar nuclei the planes and axes of reference need to be explicitly defined. Orientation of these nuclei on the basis of infratentorial brain stem axes is preferred. Comparison with published data on the chimpanzee and other anthropoid apes. The weight of the brain described herein as being 349 gm is apparently within the normal range for the adult female chimpanzee. Parker (1880) refers to data on 4, presumably adult specimens with weights of 285,376,312 and 397 gm. The first two listed were females, the sex of 89 the others was not given. Tilney ('28) used a brain weighing 350 gm for his study. This latter specimen had transverse and longitudinal dimensions of 88 and 190 mm, respectively. The specimen described here had a width of 91 mm and measured 106 mm from frontal to occipital poles. It is possible that the longer length given by Tilney was measured from the frontal pole to the caudal end of the medulla. We are not aware that figures of model reconstructions or detailed descriptions of the dentate nucleus in the chimpanzee or other anthropoid apes have been published. Tilney ('28) presents photographs of several transverse sections through the cerebellar nuclear area of the chimpanzee, orang-utan and gorilla. However, his description of the dentate nucleus is very brief and limited to the shape of the nucleus in individual sections. Comparison with published data on the human dentate nucleus. As far as is known there are figures of only two reconstructed models of the human dentate nucleus in the literature. Kappers, Huber and Crosby ('36, p. 795) present two photographs of a wax model reconstruction of an adult human dentate nucleus. The description of the model is limited to the following: "The human nucleus dentatus is a sac-like structure, the opening of which is directed medialward and frontalward. The lamellation of the mass is such that the furrows lie in the longitudinal axis of the nervous system." No measurements are given. However, the photographs are very illuminating for purposes of this comparison. Allowing for the fact that their model was of the left while the one described here is of the right nucleus the two views presented of the human dentate nucleus are strikingly similar to figures 1 and 2 of the chimpanzee nucleus. The limiting contours are almost identical. The gyral pattern differs only slightly. On the dorsolateral surface the gyri in man appear to extend in straight superior-inferior axes. In the chimpanzee these deviate slightly ventrally from superior to inferior and form a long spiral around the ventral and onto the ventromedial surfaces. The tendency for the gyri to flatten and the suki to approach each other in the inferior portion of the ventromedial surface is very similar 90 GARMAN HARLOW DARON in both models. The terminology used in their publication is somewhat confusing. The photographs are designated as medial and lateral views of the nucleus yet the tops and bottoms of the figures are labeled medial and lateral. It is possible that their figures were taken, as ours, from dorsolateral and ventromedial aspects. This would suggest their borders to be, more exactly, dorsomedial and ventrolateral. The other model of the dentate nucleus found in the literature is presented by Fowler ('01). It was constructed from serial sections of a human new born. Six photographs of the model are given. This, too, is remarkably similar to the chimpanzee model. The gyral configuration is almost identical with the model presented here, exhibiting a longitudinal pattern with the same slight ventral deviation in the inferior and lateral portion of the dorsolateral surface. Also, his description of major and minor sulci on this surface corresponds very closely with that in the chimpanzee. The shape and extent of the hilar orifice is very similar in all three models. The chimpanzee and the Kappers, Huber and Crosby models present a slightly more pronounced inferior pole than shown in the newborn specimen. Demo16 ('27) describes the gyri of the dorsal surface of the human dentate nucleus as being smaller, more sharply defined and more regular in arrangement than those in the ventral portion. He then divides the dentate nucleus into two territories, a microgyric, dorsomedially and a macrogyric, ventrolaterally. In the chimpanzee model this distinction can be made with the following qualifications. The smaller and more regularly arranged gyri occupy the superior as well as the dorsomedial portion. The larger, more irregular, and on the medial surface more flattened gyri are located inferiorly, ventrolaterally and ventral to the hilus on the medial surface. Also, as has been previously stated, the junction between these two territories is indistinct, there being a gradual transition between the two areas. A somewhat similar division of the nucleus in man has been made on the basis of staining reaction (Gans, '24) and neuronal cell types and their distribution (Hassler, '50). Hassler describes a sharp line of junction between the superior dorsomedial magnocellular and the inferior ventrolateral parvocellular portions. In a preliminary microscopic study of this specimen we have been unable to define such a sharp line of junction in the chimpanzee. Consequently, we are unable to closely correlate any histological division with the gross topography of the nucleus. The continuity of the emboliform and dentate nuclei existing in the chimpanzee is also described for the human. However, the exact site and extent of this junction is not clearly defined. Jakob ('28) states that in many places the emboliform is continuous with the dorsomedial portion of the dentate nucleus. In referring to this fusion DBjkrine ('01) considers the emboliform as an accessory dentate nucleus due to its intimate continuity with the dentate nucleus. He described this fusion as occurring in the inferior portion of the latter. In the chimpanzee the only region where the dentate and emboliform nuclei are continuous is in the inferior one-fourth of the hilar area and, as in man, in the dorsomedial portion. As can be judged from photographs of the two human models (Kappers, Huber and Crosby, '36; and Fowler, '01) the dentate and emboliform nuclei may be approximated in a manner very similar to that in the chimpanzee. However, Kappers, Huber and Crosby state that the emboliform nucleus is connected at several levels with the dentate nucleus. Fowler ('01) does not describe a confluence of these two nuclei in the human newborn. A comparison of the linear measurements of the dentate nucleus in the chimpanzee, the newborn human and the adult human may be made from the data in table 1. The length of the nucleus in the superior-inferior axis and the greatest distance between the dorsomedial and ventrolateral borders are approximately equal in the chimpanzee and the human newborn. The distance between the dorsolateral and ventromedial surfaces of the nucleus, as given for the newborn, falls within the range of this measurement in the chimpanzee. The only available linear measurements of the adult human dentate nucleus have been made along lines parallel with the three major axes of the brain stem. DENTATE NUCLEUS I N A CHIMPANZEE 91 In comparing such linear dimensions of J. S. Little) working in our laboratory usthe chimpanzee with that of the adult hu- ing the same procedure determined the man the following relationships are noted. volume of the dentate nucleus in one newIn the transverse axis measurements born and three adult human specimens. are about equal. In the dorsal-ventral The ages of the adult specimens were unaxis the figure for the chimpanzee is just known. The values obtained were 71 mm3 within the lower limit of the range of varia- for the newborn, 124 and 190 mm3for two tion given for man. In the superior-infe- adults. Separate measurements and calcurior axis the length in the chimpanzee is only 57% of that in man. Thus, the lations of the third adult specimen were principal, linear dimensional, difference made by each student. Their independent between the dentate nuclei of the chim- values were 220 and 241 mm'. This inpanzee and of the adult human is the con- formation indicates that the volume of the dentate nucleus in the adult chimpanzee siderably greater length in man. DCjCrine ('01) gives the following di- is equal to or slightly greater than that in mensions of the hilus in the adult human the newborn human. It further shows that dentate nucleus: height, 5-7 mm; length, the volume of the dentate nuclear gray 10-12 mm. The reference points used for matter is much greater in the adult human making these measurements are not given. than in the chimpanzee. In the latter In the chimpanzee a straight line between species it is only about 55% of the averthe dorsal and ventral hilar lips at the age figure given for man. This difference superior border measures 6.0 mm. This in volume can perhaps be accounted for falls within the range for the height as by the greater length of the nucleus and given by D6jCrine. The length as given greater thickness of the dentate nuclear for the adult human nucleus (10-12 mm) lamina in the adult human. probably should be compared with the SUMMARY AND CONCLUSIONS measurement made in the chimpanzee A wax model reconstruction of the denfrom the superior border to the inferior extent of the hilus along the dorsal lip tate nucleus in an adult female chimpan(8.5 mm). This greater length of the hilus zee was made from serial sections. Using in man is associated with the greater the model and the stained serial sections length of the entire nucleus in this same the following morphological information was obtained. comparison. 1. The gray matter comprising the nuThe thickness of the dentate nuclear lamina in man is frequently given as 0.3 cleus is arranged as a thin lamina which to 0.5 mm (e.g., Jansen and Brodal, '58). is disposed in gyral-like folds. This folded The thickness of this lamina in the stained lamina is grossly fashioned as the cortex sections of the chimpanzee varies from of an irregular incomplete spheroid with 0.11 to 0.20 mm. There is therefore a con- an open hilus. The hilus opens superiorly siderable difference between the two spe- and ventromedially and is bounded by cies, probably greater than could be ac- superior, dorsal and ventral hilar lips. The counted for by differences in fixation and nucleus is flattened along a dorsolateralother variances in histological technique. ventromedial axis. 2. The longitudinal axis of the nucleus As far as is known there has been only one other study made of the volume of the is nearly parallel with the same axis of dentate nucleus. Hopker ('51) gives the the brain stem. The dorsolateral surface volume determinations for both right and lies in a plane which forms an angle of left dentate nuclei in 27 human brains. approximately 30" with the transverse The values given for the right nucleus axis. range from 74 to 212 mm3, the average 3. The gyri on the dorsolateral surface being 155 mm3. This is to be compared are arranged as parallel ridges in the with the value of 84.76 mm3 for the chim- longitudinal axis. They extend inferiorly panzee nucleus. The procedure for deter- from the superior border and continue mining the volume was very similar in around onto the ventral and ventromedial both cases. Two students (V. Robards and surfaces. Dorsomedially and superiorly 92 GARMAN HARLOW DARON the gyri are narrower than elsewhere thus constituting a microgyral area. 4. There is a fusion of the dorsal margin of the emboliform nucleus with the inferior one-fourth of the dorsomedial portion of the dentate nucleus. 5. The following quantitative values are recorded. Linear dimensions of the dentate nucleus are: in the longitudinal axis, 10.7 mm; from the dorsomedial to the ventrolateral borders at their greatest separation, 9.4 mm; between the dorsolateral and ventromedial surfaces, 3.3 to 6.4 mm. The average thickness of the dentate nuclear lamina is 0.16 mm. The volume of the nuclear gray matter is 84.76 mm3. The calculated value of the area of the outer surface of the dentate nucleus is 547 mmz. A comparison of the dentate nucleus in the chimpanzee and in man led to the following conclusions. 1. As judged from wax model reconstructions the shape of the dentate nucleus in the chimpanzee is very similar to that in man. 2. The size, direction and general configuration of the gyral pattern is remarkably alike in both species. 3. The shape, position and boundaries of the hilar region are nearly identical. However, the length of the hilus in the chimpanzee is less than in man. 4. The greatest linear extent of the dentate nucleus in the transverse axis is approximately equal in the two species. In the dorsal-ventral axis the measurement in the chimpanzee is just within the lower limit of the range given for man. In the superior-inferior axis the length of the dentate nucleus in the human 1s consider- ably greater than the corresponding dimension in the chimpanzee. 5. Continuity of the dentate and emboliform nuclei occurs in both species. 6. In the chimpanzee the thickness of the dentate nuclear lamina is less than half the thickness of this lamina in man. 7. The volume of the dentate nuclear gray matter in the chimpanzee is approximately 55% of the average value given for man. LITERATURE CITED DBjBrine, J. 1901 Anatomie des centres nerveux. 11. J. Rueff, Paris. DemolB, V. 1927 Structure et connexions des noyaux dentel& du cervelet. Schweiz. Arch. Neur. Psychiat., 20: 271-294. Fowler, H. 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Barrera 1953 A method for the combined staining of cells and fibers in the nervous system. J. Neuropath. Exp. Neur., 12: 400-403. Parker, A. J. 1880 On the brain of a Chimpanzee. Med. Rec.. 17: 28-31. Tilney, F. 1928-The Brain from Ape to Man. Paul B. Hoeber, Inc., N. Y.