FLEXOR DIVISION 315 
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 flexor! (M. flexor digitalis profundus)——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.—(1) 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 humeral 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 Tendon of Tendon. of 
ulnar head (Caput ulnare) is lateral extensor common extensor 
much smaller, and is at first 
superficially situated between 
the lateral and middle flexors 
ofthe carpus. The radial head 
(Caput radiale) is the smallest, 
: ; Proximal 
and is not always present; it pouch of 
is situated on the distal two- J”! cap- 
thirds of the posterior surface Sule Taisen: 
of theradius, under the humer- —_ Branch of dean ligament 
SUSPENSOTY 
al head. Each of these heads ligament 
is provided with a tendon. The 
principal tendon—that of the 
humeral head—begins about 
three or four inches (8-10 
em.) above the carpus and is 
Digital vein 
Digital artery 
Digital nerve 
joined at the carpus by the Tendon of superficial flexor Tendon of deep flexor 
tendons of the other two heads. Fig. 285.—Cross-section oF Distat Part or Lerr METACARPUS OF 
The conjoined tendon passes Horse, Just ABpove SEesamorps. 
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).2 This is a direct continua- 
tien 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 
* 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. 
