40 



THE ARTISTIC ANATOMY OF ANIMALS 



movements of pronation and supination, the ulna is com- 

 pletely developed, for it is in its small sigmoid cavity that 

 the head of the radius revolves, and it is around its inferior 

 extremity, the head, that the corresponding extremity of 

 the radius turns. But when the movements of rotation 

 of the forearm do not exist, the inferior extremity of the 

 ulna becomes functionally useless and disappears. As to 

 its role in the movements of the region of the wrist. 



Fig. 27. — Superior Extremity of the Bones of the Forearm of 

 THE Horse : Left Limb, Superior Surface. 



I, Radius ; 2, ulna ; 3, olecranon process ; 4, coronoid process. 



that is nil, for we may remember — we will observe it again 

 when we come to treat of the articulations — that the hand 

 articulates with the radius alone (radio-carpal articulation) ; 

 this is the reason that, when the forearm possesses the 

 fullest mobility, the hand follows the movements which 

 that bone makes around the ulna. 



It is not so with the articulation at the elbow- joint ; there 

 it is the ulna, which, with the humerus, forms the essential 

 parts (humero-ulnar articulation) ; its olecranon process 



