FLEXOR DIVISION 



271 



tendon near the carpus. The ])elly of the muscle is intersected by tendinous strands, 

 and fuses more or less with that of the deep flexor. Near the carpus it is succeeded 

 by a strong, thick tendon which passes down through the carpal canal, formed by the 

 posterior ligament of the carpus, the accessory carpal bone, and the posterior 

 annular ligament (Ligamentum carpi transversum). Here it is enveloped by a 

 synovial sheath, in common with the deep flexor. This carpal sheath (Vagina 

 carpea) begins three or four inches (8 to 10 cm.) above the carpus, and extends down- 

 ward nearly to the middle of the metacarpus. Below the carpus the tendon be- 

 comes flattened and broader. Near the fetlock it forms a ring through which the 

 tendon of the deep flexor passes (Fig. 150). Here the two tendons are bound 

 down in the sesamoid groove by the posterior annular ligament, which fuses more 

 or less with the superficial flexor tendon. At the distal end of the first 

 phalanx the tendon divides into two branches which diverge to reach their points 

 of insertion, and between these branches the tendon of the deep flexor emerges 

 (Fig. 189). A second synovial sheath, the digital or sesamoidean (Vagina 



Tendon of lateral extensor Tendon of anterior extensor 



Upper pouch of joint capsule 

 Branch of suspensory ligament 



Inter sesamoid liga ment 

 Digital vein 



Fig. 197. 



'^// ~~~ Digital artery 

 '^ /^ ~^- Digital nerve 



Tendon of superficial flexor Tendon of deep flexor 

 Cross-section of Distal Part of Left Metacarpus of Horse, Just Above Sesamoids. 



digitalis), begins at the distal third of the metacarpus, three to four inches (8 to 

 10 cm.) above the fetlock, and extends to the middle of the second phalanx. 



Relations. — The belly of the muscle is related superficially to the ulnar head 

 of the deep flexor, the flexor carpi medius, and, at its origin, to the ulnar vessels 

 and nerve; deeply to the humeral head of the deep flexor. The tendon is re- 

 lated superficially to the skin and fascia; deeply to the deep flexor tendon. 



Blood-supply. — Posterior radial artery. 



Nerve-supply. — Median nerve. 



5. Deep digital flexor or flexor perforans (M. flexor digitahs profundus; 

 deep flexor of the phalanges). — The fleshy part of this muscle lies on the posterior 

 surface of the radius, under cover of the preceding muscles. It is the largest 

 muscle of the flexor group. 



Origin. — (1) The flexor (internal) epicondyle of the humerus; (2) the inner 

 surface of the olecranon; (3) the middle of the posterior surface of the radius 

 and a small adjacent area of the ulna. 



Insertion. — The semilunar crest of the third phalanx, and the adjacent surface 

 of the lateral cartilage. 



Action. — To flex the digit and carpus, and to extend the elbow. 



