Prenatal Growth of the Human Body. 135 



larger. As seen in Table IV and V, and also by the curve in Fig. 3, 

 the spinal cord declines rapidly in relative size during the 2d and 

 3d months, then more slowly throughoiit the remainder of the 

 fetal period. At birth, it forms only about .15 per cent of .the entire 

 body (average of five cases, including two of Bischoff). It is thus 

 evident that the prenatal decline in relative size is more marked in 

 the spinal cord than in the brain. In other words, prenatal growth 

 i« relatively more rapid in the brain than in the spinal cord, espe- 

 cially in the earlier part of the fetal period. After birth, the relations 

 are changed; so that the postnatal growth of the spinal cord is 

 relatively more rapid than that of the brain, as pointed out by 

 Donaldson (11) and Bonnot and Seevers (6). Vierordt gives .18 

 per cent of the total body weight for the spinal cord in the newborn, 

 and .06 per cent for the adult. 



Eyeballs. 



Aa is well knoAvn, the eyeballs are relatively large at birth, form- 

 ing, according to Vierordt, .24 per cent of the entire body weight, 

 as compared to .02 per cent in the adult. Welcker and Brandt (45) 

 cite 2 newborn in which the eyeballs formed .20 per cent and .38 

 per cent, respectively, of the entire body weight; in one fetus (6th 

 month) they formed .71 per cent and in another (3d month), .53 per 

 cent. I have made no systematic observations on the eyeballs, but in 3 

 fetuses of about the 6th month (ISTos. 210, 211 and 218), the eyeballs 

 were weighed and formed .45 per cent, .40 per cent and .39 per cent, 

 respectively, of the entire body weight. It is thus evident that they 

 are relatively larger in the fetus than at the birth; and they are 

 probably still larger in the embryo. 



Thyroid Gland. 



Although subject to considerable individual variation (cf. Tables 

 IV and V) the thyroid gland in general increases slowly but steadily 

 in relative size during the prenatal period, as shown by the curve in 

 Fig. 4 (data from Table V). In an embryo of 2 months (3.1 cm.), 

 it formed .035 per cent of the total body, increasing to .111 per cent 



