104 EFFECTS OF INANITION IN THE PREGNANT ALBINO RAT. 



the exception of Group I (in which the relative weight of the fore limbs in the tests 

 quite markedly exceeds that of the prenatal controls) , there is very little difference in 

 the relative weights in the fore limbs of the test rats and prenatal controls, in both 

 of which the fore limbs form a relatively smaller percentage of the body- weight, 

 especially in the smaller rats, than in the normal newborn. 



The absolute- weight of the fore limbs in the test rats in Group I exceeds that of 

 the prenatal controls by 34 per cent (table 5). In the other groups, however, the 

 difference between the absolute weights of the fore limbs of the test rats and pre- 

 natal controls is so irregular that it would be extremely hazardous to draw any con- 

 clusions, the average in the test rats being 8 per cent above that of the prenatal 



controls. 



The hind limbs in my prenatal controls form 5.2, 6.3, 6.8, 7.0, and 7.0 per cent 

 of the body-weight in Groups I to V, respectively (computed from table 5) . There- 

 tore, as compared with the normal newborn, the hind limbs in the prenatal controls 

 (fetuses) have a lower relative weight, and as in the case of the fore limbs, this 

 difference in relative weight is most marked in the smaller rats (fetuses) and de- 

 creases with the increase in size of the prenatal control (fetus). 



In my test rats the hind limbs form 6.7, 7.5, 7.4, 7.9, and 7.9 per cent of the 

 body-weight in Groups I to V, respectively (computed from table 5). Therefore, 

 in the test rats, the hind limbs form a higher relative percentage of the body-weight 

 than in the prenatal controls. It thus appears that in the test rats the hind limbs 

 are growing faster than the body as a whole. 



The absolute weight of the hind limbs in my test rats exceeds that of the pre- 

 natal controls in all the groups, being 36.4, 19.5, 9, 13, and 20 per cent above in 

 ( Groups I, II, III. IV, and V, respectively (table 5), the average being 19.5 per cent. 



It is to be noted that in the prenatal controls the hind limbs, as compared with 

 the fore limbs, have a lower or just equal absolute weight, and the earlier in preg- 

 nancy the fetus is removed from the mother the larger are the fore limbs as compared 

 with the hind limbs. This is in accord with the law of cranio-caudal progression in 

 growth as formulated by Jackson (1909). This also may explain the larger size 

 of the hind limbs in the test rats, since in the prenatal controls this growth tendency 

 in the hind limbs has not had sufficient time to develop, due to their shorter sojourn 

 in atero, as compared with the test rats, which, although undersized, were born at 



term. 



Jackson and Lowrey (1912), in newborn rats, found the weight of the trunk to 

 be 3.36 grams. In my newborns, the trunk weighs 3.16 grains and forms 64.4 per 

 cent of the average body-weight, 4.92 grams. In my prenatal controls the trunk 

 forms 65.2, 64.0, 63.4, 65.4, and 65.3 per cent of the body-weight in Groups I to V, 

 respectively (computed from table 5). Thus the relative weight of the trunk in 

 the prenatal controls is slighter than in the newborn rats. In my test rats the trunk 

 forms 62.7, 62.3, 62.3, 65.5, and 63.3 per cent of the body-weight in Groups I to 

 V, respectively (computed from table 5). 



Thus in the test rat the trunk has about the same relative weight as in the 

 newborn rat, while the relative weight is slightly higher in the prenatal controls 



