1 82 COMPARATIVE ANATOMY 



depression, the "mammary pocket," surrounded by a fold of skin. From 

 this condition in monotremes, the teats of the higher mammals have 

 evolved, either by elevating the milk-field at the bottom of the pocket 

 into a "true teat," as in man, or else by elevating the surrounding ridge 

 to form the "false teat" of ruminants. The number of teats corresponds 

 roughly to the number of young in a litter. 



Functional differences among the glands of vertebrates are much 

 greater than morphological, and their physiological evolution is a difficult 

 problem in biochemistry. 



Certain abnormalities in the milk glands of man, however, confirm 

 strongly the theory of the animal origin of the human body. Super- 

 numerary nipples appear in man with a certain statistical frequency. 

 But these extra teats, instead of being placed at random, are usually set 

 in two ventral rows, precisely like two rows of nipples which form the 

 milk lines of lower animals. They are, then, best interpreted as rever- 

 sions to an animal ancestor. The theory of special creation gives no 

 clue whatever to their occurrence in human beings. See Fig. 138. 



