80 



LAND MAMMALS IN THE WESTERN HEMISPHERE 



just above the trochlea, is a large, deep pit, the anconeal 

 fossa. 



The two bones of the fore-arm, the radius and ulna, are, 

 in most mammals, entirely separate from each other, but in 

 certain of the more highly specialized hoofed animals are 

 immovably coossified. Primitively, the two bones were of 



Fig. 28. — Left fore-arm bones of Wolf, 

 front side. /2., radius. L'^., ulna, ol., 

 olecranon, h., head of radius. 



Fig. 29. — Left fore-arm bones of Man, 

 front side. Letters as in Fig. 28. The 

 small object at the right of each figure is 

 the head of the radius, seen from above. 



nearly equal size, but in most of the mammalian orders there 

 is a more or less well-defined tendency for the radius to enlarge 

 at the expense of the ulna. These bones are normally crossed, 

 the radius being external at the upper end and passing in front 

 of the ulna to the inner side of the arm. The radius varies 

 considerably in form in accordance with the uses to which the 



