271 THE MUSCLES. 



It is a very delicate band, situated in front, and on the inner side of the anterior 

 extensor of the metacarpus, taking its origin, along with that muscle, from the crest 

 limiting the furrow of torsion of the humerus, behind tbe ridge; and terminating 

 within the inferior extremity of the radius by fleshy and aponeurotic fibres. This small 

 muscle can have but a very limited influence on the movements of the bones of the 

 fore-arm, because of its triiling volume. As its name indicates, it acts in supination. 



3. Short Supinator (Fig. 125, B, 2.) 

 A triangular and slightly divergent muscle, covered by the anterior extensor of the 

 metiicarpus and the commou extenaor of the digits. It has its origin in the small fossa 

 situated outside the humeral trochlea, by a flat tendon which is confounded with the 

 external lateral ligament of the elbow joint. It terminates above the anterior face and 

 the inner side of the radius, by the inferior extremities of its fleshy flbres. Covered by 

 tbe two preceding muscles, it covers the elbow articulation and the bone receiving its 

 insertion. Jt ought to be consideied, in Carnivora, as the principal supinator; it pivots 

 the radius un the ulna, so as to turn the anterior face of the first bone outwards. 



4. Round Pronator. (Fig. 125, B, 1 ; o, 1.) 



Situated on the inner and upper part of the fore-arm, between the great palmar or 

 internal flexor of the metacarpus and the interior extensor of the same ray, the rcumd 

 pronator is a thick and thort muscle, which originates on the small epicondyloid 

 tuberosity of the humerus, and terminates at the internal side of the radius by aponeu- 

 rotic flbres. 



5. Square Pronator. (Fig. 125, C, 2.) 



This muscle is situated immediately behind the bones of the fore-arm, beneath the 

 muscular masses of the posterior antibrachial region. It extends from the insertion of the 

 flexors of the fore-arm to near the carpus, and is formed of transverse flbres which pass 

 directly from the ulna to the radius. It is, then, no longer, as in Man, a square muscle 

 attached only to the lower fourth of these two bones. The two pronators are antagonists 

 of ihe short supinator, turning forwards the anterior face of the radius and metacaipus. 



COMPAKISON" OF THE MUSCLES OF THE FOKE-ARM OF MAN WITH THOSE OF ANIMALS. 



All the muscles of the fore-arm of Man are more or less perfectly represented in the 

 fore-arm of Carnivora. 



In Man, these muscles are described in placing the fore-arm in a state of supination, 

 and are divided into three regions : anterior, external, and posterior. 



A. Anterior Begion, 



This comprises eight muscles • — 



1. The round pronator, absent in animals except the Carnivora. This muscle forms 

 the internal oblique prominence in the bend of the elbow. It leaves the epitrochlea and 

 the coronoid process of the ulna, terminating on the middle third of the external face of 

 the radius. 



2. The great palmaris, which corresponds to the internal flexor of the metacarpus of 

 the Horse. Situated within the preceding, it is attached, above, to the epitrochlea ; 

 below, to the base of the second metacarpal. It is more especially a flexor of the 

 hand. 



3. The small palmaris, whose presence is not constant, and which is represented in 

 the Dog by a portion of the deep flexor of the plialanges. 



ratus ; 1', Its tendon divided at its passage behind the carpal sheath ; 2, Do., Its 

 terminal branches ; 3, Perforans ; 3', Its tendon divided after its exit from the 

 carpal sheath ; 4, Do., Its terminal branches ; 5, Tendon of the internal flexor of the 

 metacarpus; 6, Oblique flexor (anterior ulnar); 7, Inferior extremity of the long 

 supinator ; 8, Terminal tendon of the oblique extensor of the metacarpus ; 9, 

 Short abductor of the thumb; 10, Opponent of the thumb; 11, Short flexor of 

 the thumb; 12, Adductor of the thumb, transformed, in the Dog, into the adduc- 

 tor of the index ; 13, Short flexor of the small digit ; 14, Adductor of the small 

 digit; 15, Opponent of the small digit; 16,16, Metacarpal interosseous muscles; 

 a, a, a, Bands which maintain the flexor tendons on the metacarpo-phalangean 

 articulations, and limit the separation of the digits ; collectively, they represent, 

 in a rudimentary state, the palmar aponeurosis of Man. 



