FLEXOR DIVISION 



315 



Tendon of 

 lateral extensor 



Tendon of 

 common extensor 



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. — Median artery. 



Nerve-supply. — Ulnar and median nerves. 



5. Deep digital flexori (M. flexor digitalis prof undus) .—The fleshy part of 

 this muscle lies on the posterior surface of the radius, and is almost entirely under 

 cover of the preceding muscles. It is the largest muscle of the flexor group. 



Origin.— (!) The medial epicondyle of the humerus; (2) the medial surface of 

 the olecranon; (3) the middle of the posterior surface of the radius and a small ad- 

 jacent area of the ulna. 



Insertion. — The semilunar crest and the adjacent surface of the cartilage of 

 the third phalanx. 



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



Structure. — This muscle consists of three heads. The htimeral head (Caput 

 humerale) constitutes the bulk of the muscle. It is marked by tendinous inter- 

 sections, and is separable into three secondary heads. A synovial pouch from the 

 elbow joint descends under its 

 origin about two inches. The 

 ulnar head (Caput ulnare) is 

 much smaller, and is at first 

 superficially situated between 

 the lateral and middle flexors 

 of the carpus. The radial head 

 (Caput radiale) 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 humer- 

 al head. Each of these heads 

 is provided with a tendon. The 

 principal tendon — that of the 

 hmneral head — begins about 

 three or four inches (8-10 

 cm.) above the carpus and is 

 joined at the carpus by the 

 tendons of the other two heads. 

 The conjoined tendon passes 

 downward through the carpal 



canal, being included in the carpal synovial sheath with the superficial flexor ten- 

 don, as previously described. The tendon is at first broad and three-sided, but 

 becomes narrower and rounded below. Continuing downward, it is joined about 

 the middle of the metacarpus by a strong fibrous band, the so-called inferior or 

 subcarpal check ligament (Caput carpale s. tendineum) .- This is a direct continua- 

 tion of the posterior ligament of the carpus. Below this the tendon passes through 

 the ring formed by the superficial flexor tendon, then in succession over the sesa- 

 moid groove, the distal sesamoidean ligaments, and the flexor surface of the distal 

 sesamoid, to its insertion (Figs. 241 and 242). At the fetlock it widens consider- 

 ably, narrows again in the middle of the digital region, again widens at the pulley 



Proximal 



pouch of 



joint cap- 



sule 



Branch of 



suspensory 



ligament 



Intersesamoi- 

 dmn ligament 



Digital vein 

 Digital artery 

 Digital nerve 



Tendon of deep flexor 



Tendon of superficial flexor 



Fig. 2So. — Ckoss-section of Distal Part of Left ^Metacarpus of 

 Horse, Just Above Sesamoids. 



' Also commonly known as the flexor perforans or deep flexor of the phalanges. 



^ This might appropriately be termed the carpal head (caput carpale) or tendinous head 

 (caput tendineum). At its upper end it is broad, occupying the entire width of the space between 

 the small metacarpal bones; below it becomes narrower and thicker. It is related in front to 

 the suspensory ligament, and its posterior face, which is related to the deep flexor tendon, is 

 covered by the deep layer of the carpal sheath. 



