MYOLOGY 179 



spective positions occupied by these inferior insertions, it 

 must be remembered that the human forearm being in the 

 position of pronation, the tendons of the radials are attached 

 to the bases of the metacarpals nearest to the thumb — that 

 is to say, those occupying an internal position as regards 

 the fourth and fifth metacarpals. 



As its name indicates, this muscle extends the metacarpus. 

 Consequently it is, in the horse, an extensor of the canon- 

 bone. 



It is also an adductor of the hand in those animals (cat, 

 dog) in which the radio -carpal articulation, analogous 

 in form to the corresponding articulation in man, permits 

 lateral movements of the hand on the forearm. The union 

 of the fleshy bodies of the two radials is sometimes found 

 in the human species. 



Supinator Brevis. — As in the case of the long supinator, 

 the short supinator is found only in animals in which the 

 radius can be rotated to a greater or less extent around 

 the ulna ; therefore this muscle is not found in the pig, the 

 ox, or the horse ; but it forms part of the forearm of the cat 

 and the dog. 



Deeply situated at the region of the elbow, the short 

 supinator has little interest for us. All that we will say of 

 it is that it goes from the external part of the inferior ex- 

 tremity of the humerus to the superior part of the radius ; 

 and that it is, in carnivora, the essential agent in the pro- 

 duction of the movement of supination. 



Extensor Communis Digitorum (Fig. 73, 9, 10, n ; 

 Fig. 74, 10, II, 12). — Also named in veterinary anatomy 

 the anterior extensor of the phalanges, this muscle is situated 

 external to and behind the anterior extensor of the meta- 

 carpus already described. 



In the human being, the common extensor of the fingers 

 springs, in its superior part, from the bottom of a depression, 

 situated on the outer side of and behind the elbow, and limited 

 in front by the muscular prominence which the long supinator 

 and the first radial extensor form at that level. At the 

 bottom of this hollow or fossette is found the epicondyle, 

 which gives origin, amongst other muscles, to the common 



12 — 2 



