# The prenatal growth of the cat. III. The growth in length of the two extremities and of their parts

код для вставкиСкачатьTHE PRENATAL GROWTH O F THE CAT 111. THE GROWTH I N LENGTH O F T H E TWO EXTREMITIES AND O F T H E I R PARTS HOMER B. LATIMER University of Eansas FOUR FIGURES The linear growth of the fore limb, the hind limb, and the three major divisions of each appendage will be presented in this paper. All of the measurements were made on the fore limbs of the 264 specimens, but in nine of the smallest fetuses the hind limbs were so poorly developed that only the length of the entire extremity could be determined accurately. All of the measurements of the hind limb were made on the remaining 255 specimens. The four extremities were removed, as described in the first paper of this series, f o r weighing the entire extremity. After weighing, the following measurements were made. All measurements were made and recorded for both the right and the left sides, and the average of the two is meant whenever it is not otherwise stated. The arm was measured from the head of the humerus to the tip of the elbow. Next, the length from the tip of the elbow to the tip of the toes was measured. The length of the forefoot was measured from the tip of the toes to the dermal pad on the ulnar side of the wrist. This pad, according to Reighard and Jennings ( ' O l ) , marks the location of the pisiform bone, and it seemed to be the best external landmark for separating the forefoot from the forearm. In a few of the smallest specimens there was a second smaller pad proximal to this pad. The difference between these last two measurements gives the length of the forearm, and the sum of the shoulder-elbow and the elbow-toe 377 378 HOMER B. LATIMER measurements gives the total length of the fore limb. These specimens had been formalin hardened, so that it was very difficult to straighten the appendages to make a direct measurement of the total length, and so this method is more accurate than a direct measurement of the total limb length. The hind limb was measured in a similar manner. The length of the thigh was measured from the proximal part of the head of the femur to the patella. The second measurement was made from the patella to the tip of the toes, and the third was the length of the foot from the tip of the longest toe to the proximal side of the calcaneus. The total length of the limb was the sum of the first two measurements and the length of the leg is the difference between the second and the third measurements. The hind limbs were more easily and more accurately removed from the body, but the fore limbs were easier to measure accurately. The hintlfoot was flexed on the leg very frequently, so that it was hard to get the knee-toe measurement accurately, and it will be shown later that the leg length is the most variable dimension in this series of measurements. The foot was gently but firmly straightened in making the knee-toe measurement. The author wishes to gratefully acknowledge the assistance of Dr. John M. Aikman in making the measurements on the first 137 specimens. FORE LIMBS The lengths of the fore limb and of its three segments plotted on body length (nose-anus) are shown in figure 1. The dots represent the average length of the two fore limbs of the males, and the circles the average of the two limbs of the females. The distribution of the cases for the lengths of the arm, forearm, and forefoot is very similar to that for the fore limb, with no apparent sex difference jn any of the measurements, and so only the curves for the three segments are shown in t,his figure. This facilitates the comparison of the relative lengths of the parts and of the entire appendage. PRENATAL GROWTH O F THE CAT 379 The empirical formulae from which all four curves were drawn are: Fore limb, Y = 0.453 X - 7.6 Arm, Y = 0.1735 X - 3.2 Forearm, P = 0.16 X - 3.3 Y = 0.119 X - 1.3 Forefoot, I n all of these formulae Y represents the length of the part measured in millimeters, and X the body, or nose-anus, length also measured in millimeters, and plotted as the abscissae in the figure. All of these formulae are valid between 30 and 200 mm. of body length. The four curves of absolute growth Fig. 1 The growth of the fore limb plotted on body length in the upper curve with the dots representing the males, and the circles, the females. Curves are shown f o r the three segments, but the individual cases are not given. The values for the percentage curve are in the left margin, although marked ‘mni.’ The formulae f o r the four curves of linear growth are given i n the text. are all straight-line curves, or they exhibit a constant rate of increase throughout this period. The curve in this figure marked ‘percentage’ represents the total length of the fore limb expressed as a percentage of the body length. The figures in the left margin marked ‘millimeters’ serve not only to show the actual lengths, but also the percentages for this curve. On the preliminary chart all of the individual percentages were plotted and a line was then drawn through the averages for each 10 mm. in- 380 HOMER B. LATIMER crease in body length, and this line only was transferred to this figure. The distribution of the percentages about this line was fully as close as the cases about the curve in figure 1. This curve shows that the length of the fore limb increases from about 20 per cent of the body length to slightly over 40 per cent, or the length of the fore limb grows about twice as fast as the body length during the fetal period. Fig. 2 The growth of the fore limb and its segments plotted on body weight. The upper curve gives the total length with the dots representing the males, and the circles, the females. The individual cases are not shown for the three segments of the appendage. Formulae f o r all four curves are given in the text. The ordinates in the left margin, although marked ‘inni.,’ give the correct values f o r the percentage curve. Figure 1 and the computed lengths show that the forefoot is the longest part of the fore limb in the smallest specimeiis. It is surpassed first in length by the arm a t 40 mm. of body length, and at a body length of 50 mm. and over it is the shortest of the three divisions. The entire fore limb increases about 14 times. The forefoot increases a little less than 10 times, the arm about 16 times, and the forearm about 19 times. Figure 2 shows the lengths in millimeters of the fore limbs and the three parts plotted on body weight in grams. The upper curve with the dots representing the males and the PRENATAL GROWTH O F THE CAT 381 circles the females shows the linear growth of the fore limb. The lower three curves represent the linear growth of the arm, forearm, and forefoot, and, as in the preceding figure, the cases for these are not included in this figure. The curve marked ‘percentage’ represents the average percentage of the length of the fore limb of the nose-anus length plotted on body weight. It was drawn in a manner similar to the curve in figure 1. The distribution of the cases on the preliminary chart is possibly a little closer in this case, especially for the larger specimens. The figures in the left margin serve for percentage values for this curve as well as millimeters for the curves of linear growth. It is interesting to note that in the formulae for the linear growth of the fore limb and for its three parts and likewise, as will be shown later, f o r the hind limb and its three segments, the increase in length is a function of the cube root of the body weight. The formulae from which the four curves in this figure are drawn are: Fore limb, Arm, Forearm, Forefoot, Y = 14.5 VX- Qx Y = 5.8 - 0.015 X Y = 5.2 9-r-0.5 Y =4 V X I n all of these formulae Y represents the length of the extremity or its part measured in millimeters, and X, the body weight in grams from 1to 200 gm. of body weight. A comparison of the distribution of the cases in the curve of the fore limb in this figure and in figure 1 shows that there is a massing of the cases at the beginning of the curve in this figure, while in figure 1, the cases are crowded toward the end of the curve. I n other words, the body length increases more rapidly at first than the body weight, as has been shown in figure 1 of the first paper of this series. The curve representing the growth of the forefoot does not cross the other two curves as it did in figure 1. This is due to this crowding of the cases at first and also because these formulae begin at 1gm. of body weight, which excludes many of the smaller specimens. The formulae will not fit the cases below 1gm. The curves in figure 1 are more accurate for the smaller specimens. 382 HOMER B. LATIMER The percentage increments of the fore limb, and of its parts computed 011 body weight are larger a t first and decrease to smaller values than the corresponding increments computed for body lengths. This is as would be expected, since the linear dimensions increase more rapidly at first than the weight . T o derive the empirical formulae in this and the preceding papers of this series, the dimensions were plotted on a field graph; next, the average of the dimension and of the abscissa were determined f o r each 10-gm. increase in weight or each 10-mm. increase in body length. h smooth curve was drawn through as many of these average points as possible and an empirical formula developed to fit the curve. The formula was solved for each 10 units of the abscissa and plotted on the final chart, and through these points the final curve was drawn. To give an idea of the accuracy with which these curves in figures 1and 2 and also in the two following figures fit the cases, the difference between the observed length and the calculated length for each 10 mm. or 10 gm. increase in the abscissae was determined. The table giving the average linear differences for each curve and also the average percentage differences for each curve is omitted. The curve for the forearm plotted on body length has the greatest average percentage difference (5.04), and it is the only one of the six curves f o r the fore limbs which has a percentage difference exceeding 5 per cent. All three curves plotted on body length are not as well fitted to the cases as the three plotted on body weight. The smallest percentage difference of 1.65 per cent is found in the curve of fore limb length on body weight. The cat fetus resembles the human fetus in the straight-line curves of the upper extremity and its parts plotted on body length as given by Scammon and Calkins ('29) and others, and the increasing percentage of the body length resembles the changes in the percentages of the human upper extremity. The percentage values given by Scammon and Calkins ('29) are not comparable with the percentages given here, f o r these percentages are based on nose-anus length, and not crown- PRENATAL GROWTH OF THE CAT 383 rump or crown-heel lengths. No attempt will be made to discuss the rather extensive literature on the growth of the linear dimensions of the extremities of the human fetus, for this has been so well done by Scammon and Calkins ( '29). Schultz ( ' 2 6 ) finds a decrease in the growth of the human extremities in relation to the trunk height from the sixth t o the tenth fetal month and similar changes in apes and monkeys. The first part of his percentage curve rises as do the Fig. 3 Growth of the hind limb and its segments plotted on body length is shown in the upper curve. The dots represent males, and the circles, females. The individual cases are not shown for the three segments of the extremity. Formulae for the four curves are given in the text. The ordinates in the left margin give the values for the percentage curve as well as for the other curves. percentage curves for the cat extremities. His curve rises more rapidly at first and the dip toward the end is much more pronounced than in the cat fetus. I n general, the linear growth of the fore limbs of the cat fetus resembles that found in man and monkeys. HIND LIMBS The linear growth of the entire hind limb plotted on body length is shown in the upper curve in figure 3. The individual dimensions are shown as dots for the males and circles for the females. The three lowest, curves, with the individual 384 HOMER B. LATIMER cases omitted, represent the growth in length of the three parts of the hind limb. The formulae for all four curves are given below. Hind limb, Thigh, Leg, Rindfoot, Y = 0.458 X - 9.74, from 30 t o 190 mm. of body length Y = 0.165 X - 4.025, from 35 t o 200 mm. of body length Y = 0.1 X - 2.1, from 36 to 190 mm. of body length Y = 0.186 X - 3.70, from 36 t o 190 mm. of body length I n all of these formulae Y represents the length of the limb, or its part, in millimeters, and X, the body length (nose-anus) also measured in millimeters. The formulae for the parts of the extremity begin at either 35 or 36 mm. of body length, for, as has been previously stated, the hind limbs of the smallest specimens were not sufficiently developed to permit the measurement of the parts of the appendage with any degree of accuracy. This slower development of the hind limb as well as its shorter length and lighter weight (Latimer and Aikman, '31) illustrates the law of developmental direction. The distribution of the cases for the hind limb, the leg, and the hindfoot differs from the lengths of the other extremity and the other parts plotted on body length in that these dimensions in the newborn cats are longer and so are above the curve drawn for the fetuses. I n figure 3 all of the cases above 71 mm. of length represent the length of the hind limb of newborn cats. This greater length is apparent in the preliminary charts for the growth of the leg and of the hindfoot, but not for the thigh. This increase in the lengths of these dimensions is not quite as evident when the body weights are used as abscissae. I n figure 4 the cases between 121 and 160 gm. of body weight are newborn cats, and they show a rather sudden increase over the lengths of the fetuses just less than 121 gm. of body weight. All of the fetuses weighed 121 gm. or less. A possible explanation of this increase is the straightening of the ankle joint at birth. It has been stated above that it was difficultt o straighten this joint in the fetuses in order to get good measurements of these parts. This would explain the increase in the leg and the entire extremity, but it is not a satisfactory explanation for this increase in the foot length. PRENATAL GROWTH OF THE CAT 385 The percentage curve in this figure represents the lengths of the hind limbs reduced to percentages of the body lengths. The figures in the left margin represent the percentage values as well as millimeters of length. Thus the hind limb forms but about 10 per cent of the body length at first and increases to a little over 40 per cent There is a marked similarity between this curve and the percentage curve of the fore limb shown in figure 1. The greatest difference is at first, for the fore limb starts with about twice the percentage length of the hind limb. This is due, of course, to the more precocious development of the fore limb. The foot is the longest segment of each extremity at firsi. It has been shown that the forefoot is rather quickly surpassed in length by the other two segments of the fore limb, but it will be seen from figure 3 that the hindfoot remains the longest segment of the hind limb throughout the entire fetal period and also in the newborn. The leg is the shortest part and the thigh intermediate throughout the entire period. Using the computed lengths of the two extremities and their parts, it is readily seen that the entire hind limb as well as each of its parts is shorter at first and increases more in the fetal period than the fore limb or the corresponding parts of the fore limb. The hind limb increases 20.4 times in length, or nearly one and a half times the similar increase of the fore limb. The thigh increases more than any of the other parts or the two extremities. It increases over 31 times, or nearly twice the increase of the arm. The leg increases 19.9 times, which is very nearly the same as the total increase for the forearm. The hindfoot increases 17.8 times, or about one and eight-tenths times the total increase for the forefoot. The larger percentage increments (not shown) throughout the entire period for the hind limb and its segments compared to the fore limb and its homologous segments also evidence the greater growth of the hind limb and its parts. Further discussion of the relative lengths will be given later. The upper curve in figure 4 represents the length in millimeters of the hind limb plotted on body weight in grams, with 386 HOMER B. LATIMER the males shown as dots and the females as circles. The three lowest curves represent the linear growth of the three segments of this extremity. As in the preceding figures, the cases are not shown for these, as the distribution of the individual cases, as seen in the preliminary chart, is very similar to that for the entire extremity. Fig. 4 Growth of the hind limb plotted on body weight is shown in the upper curve with the dots representing the males, and the circles, the females. Individual cases are not given with the curves f o r the segments of the extremity. Formulae for the four curves are given in the text. The ordinates in the left margin give the correct value f o r the percentage curve as well as for the other curves. The empirical formulae for these four curves, like the formulae for the four curves in figure 2, are all functions of the cube root of the body weight. The formulae from which the four curves were drawn are as follows : Hind limb, Thigh, Leg, Hindfoot, Y = 16 4 X - 7.00, from 3 to 200 grams of body weight Y = 5.2 ( Y T - 1.00, from 2 to 200 grams of body weight Y = 3.1 V X + O.O16X, from 3 t o 200 grams of body weight Y = 7.1 VX--4.00, from 3 t o 200 grams of body weight Iii all of the above formulae, Y represents the length in millimeters of the extremity or its part and X represents the body weight in grams. I n every case the average percentage deviation of the calculated from the observed length is less for the curves plotted on body weight than for those having PRENATAL GROWTH O F THE CAT 387 body length as abscissae. The leg has the greatest average percentage deviation in both sets of eight curves (7.07 per cent for body length and 4.43 per cent for body weight). All but two of these curves (leg and forearm on body length) have an average percentage deviation less than 5 per cent. The lengths of the hind limb reduced to percentages of the total body length are shoKn in the percentage curve in figure 4. The numbers in the left margin, although marked millimeters, give the correct percentage values for this curve. This curve rises more rapidly at first than the percentage curve in figure 3 and it shows no decrease, as is evident at about 130 mm. of body length in figure 3. I n general, the growth of the hind limb resembles the growth of the lower extremity of the human fetus in that all curves based on body length are straight lilies (Scammon and Calkins, '29). Lkiewise, the lower extremity of the human fetus, as we have shown for the hind limb of the cat fetus, has a smaller initial length and increases more during this period. Both extremities become increasingly heavier in proportion to their length, with the greatest increase in the hind limbs. The weight in grams for each centimeter of length of the appendage was determined for both extremities for each 10-gram interval of body weight. The fore limb increased from 0.020 to 1.50 gm. per centimeter of length, or 75 times, between 0.3 and 190.0 gm. of body weight, and the similar values for the hind limb are, from 0.0216 to 1.98 gm. per centimeter of length, or an increase of 91.7 times. The marked differences in the growth of the two extremities are the greater growth of the hindfoot compared with the forefoot and the shorter leg compared with the forearm. Scammon ( '30) has shown that the percentage first derivatives for the ponderal growth of both extremities, the hands and the feet of the human fetus, are remarkably constant for the latter part of the period. The first differentials of the eight formulae for linear growth of the extremities and their parts on body weight, given above, were determined for each 10-gm. increase in body weight. These differentiah were 388 HOMER B. LATIMER then reduced to peroentages of the length in centimeters of the extremity, or part, for that body weight, or (%)IM’. The L (ern.) resulting values for the gain in length per unit of body weight were also very similar and especially for the later part of the period. The percentage differentials for the fore limb and its parts were more constant than the similar percentage differentials for the hind limb and its three segments. The percentage differentials for the leg length were less than for any of the other seven dimensions. RELATIVE GROWTH The percentages of the lengths of the fore limb and of the hind limb with reference to the body length have been shown in figures 1 and 3 plotted on body length and in figures 2 and 4 plotted on body weight. The lengths of the three segments of each appendage were reduced to percentages of the total length of the respective appendage, and plotted on body weight (curves not shown). The percentages of both the arm and forearm rise rapidly at first. The percentage lengths of the forearm in all of the cases below 1gm. of body weight average 27 per cent. This increases to 33 per cent in the second group of cases and increases but little up to birth, with a slight decrease in the newborns. The curve for the percentages of the arm length rises less than that for the forearm, f o r it averages 36 per cent for all of the cases below 1 gm. of body weight and after a rapid though brief rise it averages 37.96 per cent from 1to 120 gm. of body weight. It drops 1per cent in the newborn cats just as the curve for the forearm does. The percentage length of the forefoot decreases rapidly between the first and second groups, or from an average of 36 per cent t o 29 per cent in the second group, and then remains nearly constant. The three parts of the hind limb are not as constant in their percentages as are the parts of the fore limb. The percentages of the hindfoot average 47 per cent for the first group, or all of the specimens less than 1 gm. in bod>- PRENATAL GROWTH O F T H E CAT 389 weight. This decreases to 41 per cent in the specimens between 1and 10 gm. in weight and then slowly iiicreases to its maximum of 43 per cent. The other two segments of the extremity increase a t first a s did the two proximal segments of the fore limb, but these vary more than the parts of the fore limb. The same percentages were plotted on body length a s abscissae, and the resulting curves were practically the same as those plotted on body weight. The most striking thing shown in these percentages is the relative decrease in the percentage length of the forefeet and the hindfeet and the corresponding increase in the two proximal parts of both extremities. These changes in the earl? proportions of the extremities together with the failure of the formulae to fit the smaller specimens, which has been mentioned, would suggest that these smaller specimens belong to the embryonic rather than the fetal period, or a t least that there is some marked change in the rate of growth between these smallest specimens and the remainder of the fetuses. INDICES The ratios of the adjacent segments of the same extremity are shown in columns 2 to 5 of table 1. All of the indices in this table are the averages of the individual indices €or the specimens grouped according to body weight as shown in the first column. The number of specimens in the last three body weight groups is much smaller than in any of the others, and hence these indices are less significant. The brachial 0 0 ) rapidly at first, and to a lesser index ( f c r ~ ~ ~ ~ 2increases extent this is true of the tibio-femoral index ('?$;?). Both indices increase slowly and somewhat irregularly throughout the entire period, thus showing that the proximal segment of both extremities grows less rapidly than the middle segment. Scammon and Calkins ('29) report a similar condition for the human fetus. They find that the distal segments grow more rapidly than the middle, but this is not true for the cat fetuses, f o r the third and the fifth columns of this table show that the forefoot-forearm ( fol;eofroe~lOo) and the 390 HOMER B. LATIMER hindfoot x 100 foot-leg (--Kc) indices decrease rapidly at first and the forefoot-forearm index continues to decrease more slowly throughout the entire period. All of these indices were plotted and the distribution of the cases was very good for all of the indices, except the TABLE 1 Averages of the individual indices, for each 10 gms. of body weight, of the adjacent segments of the same errtremity and of homologous segments of the fore limb and the hind limb BODY WEIOET, GRAMS 3RAOHIAL _ _ 74.7 88.9 90.3 88.3 89.4 86.2 88.7 91.8 92.0 90.2 93.5 90.6 $32 96.4 95.4 95.5 95.2 92.7 93.0 95.7 _97.5 _ __ FOREFOOT FOREARM ~ 0.3- 1 1 - 10 10 - 20 20 - 30 30 - 40 40 - 50 50 - 60 60 - 70 70 - 80 80 - 90 90 -100 100 -110 110 -120 120 -130 130 -140 140 -150 150 -160 160 -170 170 -180 180 -190 190 -200 138.8 86.7 82.8 82.5 82.1 86.8 82.1 80.1 78.9 79.9 78.3 78.6 77.7 76.9 80.9 79.3 80.0 80.7 81.5 78.3 77.0 FOOTTIBIOLEQ REMORAL _ _ -~ 68.3 70.3 69.3 64.4 65.5 62.3 61.9 65.6 67.3 65.9 66.1 63.2 68.0 70.3 74.0 68.4 70.7 74.0 77.0 70.5 70.5 231.1 170.1 161.6 181.7 178.0 186.0 191.4 187.1 186.9 190.6 187.3 192.5 186.9 180.9 171.0 183.8 177.5 173.1 173.0 181.0 181.0 INTERMEMBRAL _ _ ~ 131.7 117.1 107.8 106.6 105.2 103.2 103.6 102.5 100.1 101.3 102.4 101.6 99.8 97.7 94.9 95.0 96.3 94.3 94.5 96.3 98.5 HUMEROFEMORAL HANDFOOT 137.2 127.2 114.2 113.6 112.6 109.5 110.7 110.4 110.3 110.4 111.1 110.3 110.0 106.8 104.3 103.0 105.0 106.0 109.0 105.7 107.0 94.9 82.8 77.3 73.2 71.5 71.3 68.8 66.9 64.5 64.9 66.2 64.7 63.5 63.2 63.7 62.3 63.5 62.0 62.0 62.3 63.0 ~~ foot-leg index. The curves are omitted t o save space. The values for this last index are probably of less significance than the others, due to the very wide variation in the indices for each group. The last three columns of this table give the average indices f o r the homologous segments of the fore limb and the hind limb. The general trend of the intermembral index (fozi+:%:g) is similar to that of the human fetus and PRENATAL GROWTH O F T E E CAT 391 the indices are shown in column 6, table 1. The average index f o r the smallest fetuses is 131.7, and Schultz ('26) gives a percentage of 132.7 for the human fetus at 9 weeks. He finds that the upper extremity is longer than the lower, except at 34 weeks of age. The fore limb of the cat is shorter for all body weights above 113 gm. The index of 94.2 per cent given by Scammon and Calkins ('29) for the newborn human is similar to that found for the newborn cat. Their values at first are lower than those given by Schultz or the indices for the cat fetus. The ponderal index ( y . ~ ~ ~ h ~) ~was b ~ computed ~ - " from table 3 of the first paper of this series and, unlike the intermembral index, it increases from 125 at 0.3 gm. of body weight to its maximum of 170.2 at a body weight of 1 gm. and then it decreases to 74.4 in the largest specimens. Next to the last column in table 1 gives the humero-femoral index ( ~ ~ K and , ~ it~ shows ~ ) that the arm is longer than the thigh throughout the entire period. The last column girforefoot x 1 0 0 ing the hand-foot index (mT) shows that the forefoot is shorter than the hindfoot in all of the specimens except a very few of the smallest, and these are probably too small to be counted in the fetal period. Another index frequently used is the ratio of the length of the extremity to the trunk length. The trunk length was not measured in these fetuses, but as a substitute for this the difference between the nose-anus length and the head length (given in the previous paper) or the spine length was used. The computed length of the fore limbs x 100 divided by this spine length was determined for each 10-mm. increase in body length. The value of this index increases from 25.8 in the smallest specimens to 53.7 at 200 mm. of body length. The similar indices for the hind limb and for the same body lengths are, 17.2 and 53.0. The increase in both indices is most rapid at first, with the greatest total increase in the hind limb-trunk index. 392 HOMER B. LATIMER SYMMETRY The asymmetry of the adult human appendages has been recognized for a long time. Recognition of this condition in the fetus is of more recent date. Bartelmee and Evaiis (’26), Schultz ( ’26 and ’30)’ and Schaeffer ( ’28) give ample discussion of the problem and good bibliographies. Table 2 gives the frequency and the percentage frequency of the occiirrence of equal lengths or of longer right or longer left measurement. There seems to be no ‘crossed symmetry,’ as suggested by Schaeffer (’as),for the total length of the appendages, for TABLE 2 Asymmetry of the eight dimenstons of the two extremities LEFT LONGER RIGHT LONGER - -- - _ _ MBASUREMENT Number 1 Per Number of eases 114 79 102 lli 114 106 121 83 of eases 1 cent .~ -~ __- - _ 114 I --45.42 Fore limb - __ Arm Forearm, Forefoot, Hind limb Thigh Leg 120 105 88 112 101 95 113 1 I 1 j 1 47.80 45.63 34.92 44.62 41.74 39.26 46.69 - S A M E LENGTH Per cent Number of eases Per cent 45.82 31.48 40.08 45.24 45.42 43.80 50.00 34.30 22 52 36 50 25 35 26 46 8.76 20.72 14.29 19.84 9.96 14.46 10.74 19.01 both limbs are longer on the left side, but not significantly so. We do find a ‘crossed symmetry’ as far as the segments of the extremities are concerned. The arm and the forearm are longer more frequently on the right side and the thigh and the leg on the left side. The left forefoot is more frequently longer (56.4 per cent of all asymmetrical cases) and the right hindfoot is longer in 57.7 per cent of the asymmetrical cases. Thus the rather marked asymmetry of the distal segment of each extremity almost seems to balance the asymmetry of the two proximal segments with a resulting very slight asymmetry of the total length of the appendages. PRENATAL GROWTH O F THE CAT 393 SUMMARY The linear growth of the fore limb and its three parts and of the hind limb and its three parts, plotted on body length, form straight-line curves. The empirical formulae for the same eight curves plotted on body weight are all functions of the cube root of the body weight. The sixteen formulae fit the cases fairly well, for the average deviation of the observed and the calculated values are all less than 5 per cent, except for the forearm and the leg plotted on body length. The curves plotted 011 body weight fit the cases better than those plotted on body length. The lengths of the hind limb, leg, and hindfoot show a marked increase in the newborn cats over the lengths in the oldest fetuses. The other dimensions continue as smooth curves into the newborn stage. The fore limb increases from about 20 to about 40 per cent and the hind limb increases from about 10 to a little over 40 per cent of the body length. The hind limb and its segments increase more in length than the fore limb and the homologous parts of the fore limb. The hind limbs become heavier per unit of length, and to a somewhat lesser degree this is true of the fore limbs. After a body weight of 10 gm. is attained, the relative lengths of the segments of each extremity change but slightly with reference to the length of the entire extremity. I n the smaller specimens the percentages of both forefeet and hindfeet drop rather rapidly, while the lengths of the other parts increase, with the exception of the leg, which does not change as much as the others. The indices of the adjacent segments of the same extremity show that the middle segment of each extremity, in general, grows more rapidly during the fetal period than the most proximal segment. The forefoot-forearm index decreases during the fetal period. The intermembral, the humero-femoral, and the hand-foot indices all decrease, rapidly at first, and then more slowly until the newborn stage. 394 HOMER B . LATIMER The two extremities do not show a significant asymmetry, but all of the segments of the extremities show a ‘crossed symmetry. ’ L I T E R A T U R E CITED AKIBA, TAKASHI1924 Uber die Korperproportionen der japanisehen Feten. Folia Anat. Japonica, Bd. 2, S. 189-219. LATIMER, H. B., AND JOHN M. AIKMAN 1931 The prenatal growth of the eat. I. The growth in weight of the head, trunk, fore limbs, and hind limbs. Anat. Ree., vol. 48, pp. 1-26. LATIMER, H. B. 1931 The prenatal growth of the eat. 11. The growth of the dimensions of the head and trunk. Anat. Rec., vol. 50, pp. 311-332. REIGHARD, JACOB, AND H. S. JENNINGS 1901 Anatomy of the eat. Ncw York. S r A M N o N , RICHARDE. 1925 Section on developmental anatomy. Morris ’ Textbook of Anatomy, edited by C. M. Jackson. 1930 The ponderal growth of the extremities of the human fetus. Am. J. Phys. Anthrop., vol. 15, pp. 111-121. SCAivhiON, R. E., AND L. A. CALKINS 1929 The development and growth of the external diniensions of the human body in the fetal period. The University of Minnesota Press. SCHAEFFER, A. A. 1928 Spiral movement i n man. J. Morph. and Physiol., v01. 4c7, pp. 293-398. SCHULTZ, ADOLPH H. 1926 Fetal growth of man and other primates. Quart. Rcv. Biol., vol. 1, pp. 465- 521. 1930 The skeleton of the trunk and limbs of higher primates. Human Biol., vol. 2, pp. 303-438.

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