_1_, Large metacarpal bone; _2_, distal end of small metacarpal bone;
_3_, fetlock joint; _5_, first phalanx; _6_, pastern joint; _7_,
second phalanx; _8_, coffin joint; _9_, third phalanx; _11_, lateral
cartilage; _11′_, upper (subcutaneous) border of cartilage; _12_,
suspensory ligament; _13_, branch of _12_ to extensor tendon; _14_,
deep flexor tendon; _15_, superficial flexor tendon; _15′_, 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. für Künstler.)
]
_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.