cushion; _c_, semilunar sinus of os pedis.]

THE FLEXOR PEDIS PERFORANS, OR THE DEEP FLEXOR OF THE PHALANGES.--This
muscle consists of three easily-divided portions: an ulnar, a humeral, and
a radial, and has for points of origin the olecranon process of the ulna,
the inner condyloid ridge of the humerus, and the posterior surface of the
radius. These portions are continued by a common tendon which enters the
carpal sheath with the tendon of the perforatus, and continues with it
through the synovial sheath of the metacarpo-phalangeal region. Like the
last-named tendon, it receives a supporting check-band, in this case from
the posterior ligament of the carpus. Passing down between the suspensory
ligament in front, and the perforatus tendon behind, it glides over the
sesamoid pulley and passes through the ring formed by the perforatus.
Continuing its course, it passes between the bifurcating portions of the
extremity of the perforatus, glides over the smooth posterior surface of
the supplementary glenoid cartilage of the articulation of the first and
second phalanges, plays over the inferior surface of the navicular bone,
and finally becomes inserted into the semilunar crest of the os pedis. On
reaching the posterior border of the navicular bone it widens out to form
the plantar aponeurosis.

In connection with the lower portion of this tendon must be noticed the
Navicular Sheath. This is a synovial sheath lining the deep face of the
tendon, and reflected on to the navicular bone and the interosseous
ligament of the pedal joint. This will be of particular interest when we
come to deal with cases of pricked foot from picked up nails. Above, it is
in connection with the synovial membrane of the pedal articulation and that
of the metacarpo-phalangeal sheath.

_Action_.--The action of the perforans is to flex the third on the second,
and the second on the first phalanx. The latter it flexes in turn on the
metacarpus. It also assists in the flexion of the entire foot on the
forearm, and in supporting the angle of the metacarpo-phalangeal
articulation when the animal is standing.

D. THE ARTERIES.

So far as the arteries supplying the foot are concerned, we shall be
interested in following up the distribution of the two digitals, which are
the terminal branches of the Large Metacarpal.

THE LARGE METACARPAL, OR COLLATERAL ARTERY OF THE CANNON.--This, the larger
terminal branch of the posterior radial artery, needs brief