XV.] PRIMATES. 247 



lower end of the radius ; and also, though not very directly, 

 with the upper surface of the carpus. By the side of this is 

 a small conical process, the ulnar styloid process. 



The movement of these bones upon the humerus at the 

 elbow-joint is simply that of a hinge, formed mainly by the 

 articular surface of the ulna. In pronation and supination, 

 which is more free and complete than in any other Mammal, 

 the ulna is stationary, and the radius moves ; the upper end 

 only on its own axis, being fixed to the side of the ulna by 

 the annular ligament,, but the lower end rotates round the 

 lower end of the ulna, carrying the hand with it. 



The higher Apes have the axis of the humerus almost as 

 much twisted on itself as in Man ; and they also, almost 

 alone among Mammals, resemble Man in not having the 

 olecranon process of the ulna prolonged upwards beyond 

 the sigmoid notch. Even in the Baboons these special 

 anthropoid characters are lost. The humerus has no supra- 

 condylar perforation in any of the Old World Siniiiua, nor in 

 Ateles, Mycctes or Hapale among the American Monkeys ; 

 but in the remaining genera of CcbidcE, and in most of the 

 Lemurs, such a perforation is found. In the Aye-Aye 

 iyChiroiiiys) the supinator ridge is remarkably developed. 

 The radius and ulna are distinct in all ; in the higher forms 

 (especially the Gorilla) greatly curved, leaving a large space 

 between them in the middle of the fore-arm. The power 

 of supination and pronation, which in the hi/her forms 

 almost equals that enjoyed by Man, is much reduced in 

 the inferior types of the order, although never entirely lost. 



In the Carnivora the head of the humerus has no 

 longer that hemispherical form, so well marked in the higher 

 Primates. The tuberosities are strong and rough, and 

 project upwards beyond the level of the head. The shaft 

 is much curved forwards. The deltoid ridge is strong, and 



