22 DISEASES OF THE HORSE’S FOOT 
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 sup- 
porting 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. 
Tue Larce Meracarpan, oR CoLLATERAL ARTERY OF THE 
Cannon.—This, the larger terminal branch of the posterior 
radia] artery, needs brief mention, for the reason that we 
