THE SKELETON IN MAMMALIA. THE MANUS. 503 



In the INSECTIVORA the arm bones are well developed, and 

 the radius and ulna, though sometimes united, are generally 

 distinct ; as a rule there is an ent-epicondylar foramen, but this 

 is absent in the Hedgehog. The Mole has an extraordinary 

 humerus, very short and curved, and much flattened and ex- 

 panded at both ends. It articulates both with the scapula 

 and coraco-clavicle. The ulna has a greatly developed ole- 

 cranon. 



In the CHIROPTERA both humerus and radius are exceed- 

 ingly long and slender ; the ulna is reduced to little more than 

 the proximal end and is fused to the radius. There is no ent- 

 epicondylar foramen. 



All PRIMATES have the power of pronation and supination 

 of the fore-arm, by the rotation of the distal end of the radius 

 round that of the ulna. 



In Man and the Anthropoid Apes the humerus is long and 

 straight, and has a globular head ; neither of the tuberosities, 

 nor the deltoid nor supinator ridges are much developed. The 

 olecranon fossa is deep and there is no ent-epicondylar fora- 

 men. The radius is curved and has a narrow proximal, and 

 expanded distal end, the ulna is straighter than the radius 

 and has the distal end much smaller than the proximal ; the 

 olecranon is not much developed. 



In the lower Primates, although the radius and ulna are 

 always quite separate, the power of pronation and supination 

 is not nearly so great as in the higher forms. In most of the 

 Cebidae and Lemurs an ent-epicondylar foramen occurs. 



THE MANUS. 



The Manus is divisible into two parts, viz. the carpus or 

 wrist, and the hand which is composed of the metacarpals and 

 phalanges. The carpal bones are always modified from their 

 primitive arrangement, sometimes more, sometimes less. One 

 modification however is always found in mammals, viz. the 



