THE BONES 75 



Extremities. 



Next in importance to the head and vertebral column, as 

 regards distinctive human characters, come the extremities. 



In the first place, the head of the humerus differs widely 

 from that of the anthropoids and other mammals. The head of 

 the human humerus is almost a perfect segment of a sphere ; 

 that of the gorilla, according to Aeby, is like a transversely 

 placed cycloid. In mammals, as a rule, the articular cavity 

 of the scapula is placed downwards, in man it has an outward 

 direction. In the quadrupeds, the head of the humerus during 

 walking is pressed into the joint ; in man, the head is free, 

 thus rendering a backward and forward rotatory motion 

 possible, in addition to the up and down motion. Another 

 distinctive character of man is the length of the humerus, which 

 in the human body is shorter, but in the anthropoid longer than 

 the femur. Man in his more highly developed state is further 

 distinguished from the anthropoids by the shortness of the fore- 

 arm in proportion to the upper arm (see Fig. 34). 



According to Wiedersheim, taking the humerus at 100, the 

 length of the radius is as follows : 



In the European . . . -'73 

 Aino . . 77-4 



Veddah .... 80 



Chimpanzee .... 90^94 

 In the gibbon the forearm even exceeds the upper arm in length, 

 and to this the fact is due that in an erect position the finger- 

 tips touch the ground. The perforation of the fossa olecrani, 

 peculiar to the anthropoids and lower apes, occurs very seldom 

 in the higher races of man, but its absence cannot rank as an 

 absolutely distinctive character, since it is frequently observed 

 in the lower races (S. Africans, Veddahs) and occurs in pre- 

 historic skeletons. " In man the fore-foot, fitted exclusively 

 into the radius and thus rendered movable, has developed into 

 the hand" (Pfitzer). The rare cases where an articulatio ulno- 

 carpea occurs (i.e., where the ulna is connected with the tra- 

 pezium and pisiform) must be regarded as cases of atavism. 1 



In man the os centrale, which appears in the embryo, 



1 Wiedersheim, loc. cit., p. 85. 



