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 coiEn 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 

 homy 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 jcints 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 tipper 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 XXXIII, fig. 5.) 



