Prenatal Growth of the Human Body. 120 



total volume. In no specimen examined by me does the head exceed 

 the trunk in size, though it sometimes approaches it closely. 



The steady decrease in the relative size of the head from the 2d 

 month onward is in part due to a corresponding decrease in the 

 relative size of the brain (which will be described later). As the 

 brain throughout bears a fairly constant ratio to the volume of the 

 head (somewhat less than half), however, it would appear that the 

 facial* portion of the head must also decrease in relative size at about 

 the siame rate as the brain. This does not agree with the conclusion 

 of Merkel (32), who found the facial portion of the head of about 

 the same relative size in a series of fetuses of different ages, excepting 

 the youngest (3d month), where the face was relatively larger. 



In the adult, according to Meeh's (31) observations, the head 

 forms from 6 per cent to 11 per cent of the total body volume; or, 

 according to Harless (18), 6 per cent to 9 per cent of the total body 

 weight. 



Trunk. 



In Fig. 2, the curve of the relative growth of the trunk is not repre- 

 sented, in the 1st month. Since, however, the extremities are very 

 small at this time, it is evident that the trunk must be relatively 

 very large. When the head forms 35 per cent of the body, the trunk 

 would necessarily form nearly 65 per cent. At the beginning of the 

 2d month, as is shown by the curve, the trunk has decreased in 

 relative size, so that it forms about 50 per cent of the total body 

 volume. From the 2d month onward, the trunk continues to de- 

 crease (somewhat irregularly) in relative size. During the first half 

 of the fetal period, the curve of relative growth of the trunk descends 

 nearly parallel with that of the head. The curves diverge in the 

 second half of the fetal period, however, that of the trunk remaining 

 on the whole nearly horizontal, fluctuating between 40 per cent and 

 45 per cent. 



Meeh (31) separated the trunk from the lower extremities by a 

 horizontal section at the level of the perineum, which apparently 

 adds about 6 per cent to the relative size of the trunk. The average 

 in 8 adults measured by him is about 54 per cent, Avhich would cor- 



