22 DISEASES OF THE HORSE'S FOOT 



sheath of the metacarpophalangeal 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 car- 

 tilage 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 metacarpophalangeal 

 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 metacarpophalangeal 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 mention, for the reason that we 



