370 DISEASES OF THE HORSE. 



The sufraff/7u.s is a very compact bone, set in an oblique direction 

 downAvard and forward, and extends from the cannon bone to the 

 coronet. 



The coronet is a short, cube-shaped bone, set between the suffraginis 

 and coffinbone, in the same oblique direction. 



The nariculat' bone is short, flattened above and below, and is 

 attached to the coffin bone behind. 



The coffin hone forms the end of the foot and is shaped like the 

 horny box in which it is inclosed. 



All of these bones are covered on the surfaces which go to make up 

 the joints with a cartilage of incrustation, while the portions between 

 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 inclosing the 

 joints. 



The fetlock joint is maae by the union of the lower end of the can- 

 non and the uj^per 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 — demands 

 special mention. 



The siispensory ligament of the fetlock starts from the knee, ex- 

 tends down behind the cannon, lying behind the two splint bones, 

 until near the fetlock, w^here it divides and sends a branch on either 

 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 XXXII, 

 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 a 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 XXX, fig. 5.) 



The flexor pedis perforans^ or deep flexor of the foot, passes down 



