Prenatal Growth of the Human Body. 



141 



In the adult, it is well known that the left kidney is larger than 

 the right in the great majority of cases (cf. data by Thoma). Beneke 

 (4) from obsen^ations on only a few cases concluded that at birth 

 the kidneys are approximately equal in size, no difference being 

 appreciable until after the 3d month (postnatal). The data col- 

 lected by me, however, demonstrate that the predominance of the left 

 kidney extends back to the early embryonic months. As to the cause 

 of the smaller size of the right kidney, it is probable that its growth 

 is retarded by the greater pressure of the liver on the right side. 

 This conclusion is strengthened by the fact that (as will be shown 

 later) the right suprarenal gland is also usually smaller than the left. 



The Wolffian bodies are relatively large in the early embryo, form- 

 ing .60 per cent of the total body volume in an embryo of the 5th 

 week (11 mm.), in which the renal anlages are just appearing. As 

 the kidneys enlarge, the Wolffian bodies become not only relatively 

 but absolutely smaller, as shown by measurements on the following 

 three specimens: 



Suprarenal Glands. 



As is evident in Fig. 4, the curve of growth of the suprarenal glands 

 is quite different from that of the kidneys. During the 2d month, 

 when they first become definitely outlined, the suprarenal glands form 

 about .3 per cent of the total body volume (Tables IV and V). They 

 increase rapidly to a maximum of about .46 per cent in the 3d month, 

 decreasing steadily thereafter in relative size. In the full-term 

 still-born, they form an average of .246 per cent of the total body 

 weight (108 cases), and in the live-born .229 per cent (101 cases). 

 Vierordt gives .23 per cent for the suprarenals in the newborn, and 

 .01 per cent in the adult. 



