338 THE MUSCLES. ' 



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

 musculo-spiral groove of the humerus, behind the 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 forearm, because of its trifling 

 volume. As its name indicates, it acts in supination. 



3. Short Supinator (Fig. 188, b, 2). 

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

 carpus and the common extensor of the digits. It has its origin in the soiall fossa situated 

 outside tlie 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 fibres. Covered by the two preceding muscles, 

 it covers the elbow articulation and the bone receiving its insertion. It ought to be considered, 

 in Carnivora, as the principal supinator; it pivots the radius on the ulna, so as to turn the 

 anterior face of the first bone outwards. 



4. Round Pronator (Fig. 188, b, 1 ; c, 1). 

 Situated on the inner and upper part of the forearm, between the great palmar or internal 

 flexor of the metacarpus and the mterior extensor of the same ray, the round pronator is a 

 thick and short muscle, which originates on the small, epicondyloid tuberosity of the humerus, 

 and terminates at the internal side of the radius by aponeurotic fibres. 



5. Square Pronator (Fig. 188, o, 2). 

 This muscle is situated immediately behind the bones of the forearm, beneath tlie muscular 

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

 forearm to near the carpus, and is formed of transverse fibres 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 the short supinator, 

 turning forwards the anterior face of the radius and metacarpus. 



Comparison of the Muscles of the Forearm of Man with those of Animals. 



All the muscles of the forearm of Man are more or less perfectly represented in the forearm 

 of Carnivora. 



In Man, these muscles are described in placing the forearm in a state of supination, and 

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



1. Anterior Region. 

 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, the presence of which is not constant, and is represented in the Dog 

 by a portion of the deep flexor of the phalanges. 



4. The superficial flexor or perforatus has two planes of muscular fibres. The superficial 

 plane is destined to the tendons of the medius and annularis ; the deep plane to the tendons 

 of the index and little finger. These tendons are fixed into the secondary phalanges of the 

 above-named digits. 



5. The anterior ulnar resembles the oblique flexor of the metacarpus of the Horse. It is 

 inserted, above, into the epitrochlea and the olecranon; below, in the pisiform bone. Its 

 action is transmitted, by a fibrous band, from this bone to the fifth metacarpal. It flexes the 

 hand by inclinin"; it inwards. 



6. The deep flexor or perforans is resolved into two fasciculi : one, the internal, for the little 

 finger, the annularis, and the medius; the other, the external, for the index. The three first 

 tendons are at first united to each other by fibrous bands, and together pass through a sheath 

 formed by the perforatus. 



7. The proper flexor of the thumb, represented in the Dog by the radial portion of the 

 perforans. It is attached, for one part, to the upper three-fourths of the anterior face of the 

 radius, the interosseous aponeurosis, and the coronoid process of the ulna ; on the other part, 

 to the second phalanx of the thumb. 



