HUMAN EVOLUTION 



531 



of man's kinship with lower animals. The direction of growth of 

 the hair on the arms and hands resembles that of the tailless apes, 

 in which it is related to the shedding of water when the arms 

 are clasped above the head with the elbows pointing downward. 

 The vermiform appendix is a structure that is vestigial in man. 

 It is larger in the apes and functional in some mammals. The 

 Darwin's point (Fig. 286) that occurs in some human ears is inter- 

 preted as a reversion to a condition showing the inturned point of 

 an ape-like ear. Rudimentary muscles that move ears and scalp 

 in man, the rudiment of a nictitating membrane at the inner 



^-C^- 



/ 



Fig. 287. — Human embryo in three stages, .showing rudimentary gill-slits, 

 tail, and limbs, and development in later stages. 



(Adapted from Mall, and drawn by Wiley Crawford.) 



corner of the eye, and the pineal body of the brain, which is homolo- 

 gous with the median eye of some reptiles, notably the lizard 

 Hatteria, are further examples. Many other instances of less 

 famiUar structures could be given. The argument here is the same 

 as elsewhere. The rudimentary digits on the fore limb of a horse 

 can be explained if we suppose that horses descended from ancestors 

 with more than one digit. The complete set of bones of a fore 

 limb in the flipper of a whale or seal are reasonably there, if it is 

 supposed that seals and whales came from ancestors in which these 

 parts functioned like the fore limbs of land vertebrates. So the 

 argument runs with man. It is said by competent anatomists 

 that there are no less than seventy vestigial relics of ancestry that 

 can be easily recognized in the adult human body. 



What may be called embryonic vestiges are even more numerous. 

 Rudimentary gill sUts and a fish-like blood system are formed 



