i86 THE ARTISTIC ANATOMY OF ANIMALS 



brachialis in zoological anatomy, and that veterinary 

 anatomists give it the name of small extensor of the fore- 

 arm.'^ 



In the dog it recalls, as to position, the human anconeus, 

 but with this difference — that, in the latter, the anconeus, 

 triangular in outline, has one of its angles turned outwards 

 (the epicondyloid attachment) and one of its sides turned 

 towards the olecranon. Here it is entirely the opposite. 

 The anconeus, similarly triangular, is broader externally. 

 At this level it takes its origin from the external border of 

 the humerus, the epicondyle, and the external lateral liga- 

 ment of the articulation of the elbow ; thence its fibres 

 converge towards the external surface of the olecranon, to 

 be there inserted. 



It is in relation, anteriorly and inferiorly, with the posterior 

 ulnar muscle. It is covered superiorly by the external head 

 of the triceps. In the cat the disposition of the anconeus 

 is analogous. But in the other quadrupeds with which we 

 are here concerned it is completely covered by the ex- 

 ternal head of the triceps. It really participates in the 

 formation of the triceps ; and seeing that it takes origin from 

 the posterior surface of the humerus at the margin of the 

 olecranon fossa (Fig. 72), and proceeds thence towards the 

 olecranon to be inserted, we can understand why veterinary 

 anatomists have connected its study with that of the 

 posterior muscular mass of the arm. 



This muscle is an extensor of the forearm on the arm. 



We proceed now to inquire what the deep muscles of the 

 posterior region of the human forearm become in quadru- 

 peds : the long abductor of the thumb, the short extensor 

 of the thumb, the long extensor of the thumb, the proper 

 extensor of the index. We know that in every instance 

 these muscles, which are deeply seated at their origin, 

 become superficial afterwards. 



In quadrupeds, on account of the position in which the 

 forearm is placed — viz., pronation — the corresponding 

 muscles occupy the anterior aspect of this region. 



Long- Abductor of the Thumb {Extensor ossis mctacarpi 



* It is also called by some authors, the small anconeus. 



