272 



FASCIA AND MUSCLES OF THE HORSE 



Structure. — This muscle consists of three principal heads. The humeral head 

 (Caput humerale) constitutes the bulk of the muscle. It is marked ])y tendinous 

 intersections, and is separable into three secondary heads. The ulnar head (Caput 

 ulnare, ulnaris accessorius) is much smaller, and is at first superficially situated be- 

 tween the outer and middle flexors of the carpus. The radial head (Caput radiale, 

 radialis accessorius) is the smallest, and is not always present; it is situated on the 

 distal two-thirds of the posterior surface of the radius, under the humeral head. Each 

 of these heads is provided with a tendon. The principal tendon — that of the humeral 



head — begins about three or four inches (8 

 to 10 cm.) above the carpus. It is soon 

 joined by the small tendon of the ulnar 

 head, which begins about the middle of the 

 forearm. The tendon of the radial head 

 fuses with the principal tendon close to 

 the carpus. The conjoined tendon passes 

 downward through the carpal canal, being 

 included in the carpal synovial sheath 

 with the superficial flexor tendon, as 

 previously described. Continuing down- 

 ward, it is joined about the middle of the 

 metacarpus by a strong fibrous band, the 

 so-called inferior or subcarpal check liga- 

 ment (Caput tendineum) . This is a direct 

 continuation of the posterior ligament of 

 the carpus. Below this the tendon passes 

 through the ring formed by the perfor- 

 atus, then in succession over the sesamoid 

 groove, the inferior sesamoidean liga- 

 ments, and the tendon surface of the third 

 sesamoid, to its insertion (Figs. 150 and 

 151 ). Its terminal part is much widened. 

 From the distal third of the metacarpus to 

 the distal end of the second phalanx it is 

 inclosed in the digital synovial sheath de- 

 scribed in connection with the perforatus. 

 The navicular bursa or bursa podotroch- 

 learis is found between the tendon and 

 the third sesamoid or navicular bone. 

 The terminal part of the tendon is bound 

 clown by the fibrous sheet descrilDed with 

 the fascia. 



Relations. — The belly of the muscle is 

 related posteriorly to the perforatus and 

 the middle flexor of the carpus; internally, 

 to the internal carpal flexor, the radial 

 check ligament, and the posterior radial 

 vessels and median nerve; externally, to the external flexor of the carpus; anteriorly, 

 to the radius and ulna and branches of the posterior radial artery and median nerve. 

 Below the carpus the tendon is accompanied by the vessels and nerves of the digit. 

 It may also be noted that the muscle is not entirely covered by the other flexors ; it 

 comes in contact with the skin and fascia on the postero-external aspect of the 

 proximal half of the forearm, and also on the outer aspect of the distal fourth. 

 Blood-supply. — Posterior radial and ulnar arteries. 

 Nerve-supply. — Median and ulnar nerves. 



Fig. 198. — Dioit of Horse, Lateral View. 

 1, Large metacarpal bone; 2, distal end of small 

 metacarpal bone; 3, fetlock joint; 6, first phalanx; 6, 

 pastern joint; 7, second phalanx; 8, coffin joint; 9, 

 third phalanx; 11, lateral cartilage; 11', upper (sub- 

 cutaneous) border of cartilage; 12, suspensory liga- 

 ment; 13, branch of 12 to extensor tendon; 14, deep 

 flexor tendon; ^5, superficial flexor tendon; i5', branch 

 of 15; 16, posterior annular ligament of fetlock; 17, 

 proximal annular or vaginal ligament of digit; 18, 

 distal annular ligament or reinforcing sheath of deep 

 flexor tendon; 19, lateral ligament of coffin joint; 21 , 

 tendon of common or anterior extensor; 22, tendon of 

 lateral extensor; 23, digital vein. (After Ellenberger- 

 Baum, Anat. fiir Ktinstler.) 



