396 DISEASES OF THE HORSE. 
The large pastern is a very compact bone, set in an oblique direc- 
tion downward and forward, and extends from the cannon bone to 
the coronet. 
The coronet is a short, cube-shaped bone, set between the large 
pastern and coffin bone, in the same oblique direction. 
The navicular bone is short, flattened above and below, and is 
attached to the coffin bone behind. 
The coffin bone forms the end of the foot and is shaped like the 
horny box in which it is inclosed. 
_ All these bones are covered on the surfaces which go to make up 
the joints with a cartilage of incrustation, while the portions be- 
tween are covered with a fibrous membrane called the periosteum. 
The joints of the legs are of especial importance, since any inter- 
ference with their function very largely impairs the value of the 
animal for most purposes. As the joints of the foot and ankle are 
at the point of greatest concussion they are the ones most subject to 
injury and disease. 
There are three of these joints—the fetlock, pastern, and coffin. 
They are made by the union of two or more bones, held together by 
ligaments of fibrous tissue, and are lubricated by a thick, viscid 
fluid, called synovia, which is secreted by a special membrane inclos- 
ing the joints. 
The fetlock joint is made by the union of the lower end of the 
cannon and the upper end of the large pastern bones, supplemented 
by the two sesamoids, so placed behind the upper end of the pastern 
that the joint is capable of a very extensive motion. These bones are 
held together by ligaments, only one of which—the suspensory—de- 
mands special mention. 
The suspensory ligament of the fetlock starts from the knee, ex- 
tends down behind the cannon, lying behind the two splint bones, 
until near the fetlock, where it divides and sends a branch on each 
side of the joint, downward and forward, to become attached on 
the sides of the extensor tendon at the lower end of the pastern bone. 
As it crosses the sesamoids, on the posterior borders of the fetlock, it 
throws out fibers which hold it fast to these bones. (Plate XXXIV, 
fig. 2.) 
The pastern joint is made by the union of the two pastern bones. 
The coffin joint is made by the union of the small pastern, coffin, 
and small sesamoid, or navicular bones, the latter being set behind 
and beneath the joint surface of the coffin bone in such way as to 
receive largely the weight of the small pastern. 
Three tendons serve to move the bones of the foot one on another. 
Two of these flex, or bend, the joints, while the other extends, or 
straightens, the column of bones. (Plate XX XIII, fig. 5.) 
