124 LAWSON G. LOWREY 



2. Relative growth of the viscera 



Under this heading will be considered the relative growth of 

 all the viscera together (including the brain and spinal cord, 

 and excluding the contents of the stomach and intestines) which 

 were measured. In a negative way, this gives also the relative 

 growth of the other structures of the body, chiefly skeleton, mus- 

 culature and skin. 



A reference to fig. 1 will show the general trend of the curve. 

 The maximum relative size occurs in the 15 mm. litter, where all 

 the visceral organs form 38.08 per cent of the total body. At 

 58 mm. they form 36.65 per cent, and in the late fetus, 16.23 

 per cent of the total weight. In the adult, they form only 7.85 

 per cent of the total weight. 



From this it is evident that the skeleton and musculature are 

 relatively small at first, increasing at first rapidly, then more 

 gradually, until, in the adult, they form about one half more 

 relatively than they did at the fetal maximum for the organs. 

 This is based on the assumption that there is relatively little 

 change in the relative weight of the skin, etc. 



Corresponding figures for the human show that the viscera form 

 about 36 per cent of the total body in the second fetal month, 

 slowly decreasing to about 26 per cent at birth, reaching about 

 13 per cent in the adult. 



The total relative weight of the viscera is apparently about the 

 same for the pig and human in early fetal life; but at birth that 

 for the pig is much below the human. The decrease for the vis- 

 cera and the increase in relative size of the remaining structures 

 are very marked between birth and maturity, both in the pig and 

 the hiunan. 



According to Jackson, the brain and spinal cord in the human 

 embryo, at the beginning of the second month, have nearly three 

 times the volume of the organs lying ventral to the body axis; 

 at birth they are about equal; while in the adult, the ventral 

 organs are six times as large as the brain and spinal cord. In 

 the pig, the nervous system is relatively much smaller. In the 

 18 mm. litter, the ventral organs are nearly three times as large 



