metacarpo-phalangeal sheaths, and, arriving behind the fetlock, forms a
ring for the passage of the flexor perforans. Its termination is bifid, and
it is inserted on either side to the lateral surface of the second phalanx.

[Illustration: FIG. 11.--THE FLEXOR PERFORANS AND FLEXOR PERFORATUS
TENDONS. The metacarpo-phalangeal sheath and the ring of the perforatus
laid open posteriorly, and the cut edges reflected to show the passage
of the perforans. 1, Reflected cut edges of the perforatus ring and the
metacarpo-phalangeal sheath; 2, the perforans tendon; 3, point of insertion
of the perforans tendon into the semilunar crest of the os pedis (this
widened and thickened extremity of the perforans is known as the plantar
aponeurosis).]

[Illustration: FIG. 12.--THE FLEXOR PERFORATUS AND FLEXOR PERFORANS
TENDONS. The metacarpo-phalangeal sheath and the ring of the perforatus
laid open posteriorly, and the cut edges reflected; the flexor perforans
cut through at about the region of the sesamoids, and its inferior portion
deflected. 1, Superior end of severed perforans tendon; 2, inferior end of
severed perforans tendon; 3, insertion of flexor perforans into
semilunar crest of os pedis; 4, the cut and reflected edges of the
metacarpo-phalangeal sheath and perforatus ring; 5, the bifid insertion of
the flexor perforatus into the lateral surfaces of the os corona; 6,
the capsular ligament of the pedal joint; 7, the navicular bone; 8, the
posterior surface and glenoid fibro-cartilage of the os coronæ.]

_Action_.--This muscle flexes the second phalanx on the first, the first on
the metacarpus, and the entire foot on the forearm. Mechanically, it
acts as a stay when the animal is standing by maintaining the
metacarpo-phalangeal angle.