134 ELEMENTS OF HIPPOLOGY. 



the pus accumulates it is forced upward usually until the sinus 

 reaches the rim of the coronary band, where an open sore re- 

 sults. Such a sore, a fistula, is called a quitter. Frequently, 

 in the history of quittors, the sole is finally penetrated by the 

 pus, and natural drainage results. A quittor is almost always 

 the result of neglect, and in its most frequent form is the result 

 of a neglected tread. 



Cracks in the hoof running up and down are termed sand- 

 cracks when in the toe — usually in the hind feet, and quarter- 

 cracks when on the inside — usually on the front feet. The 

 outside of the feet is seldom cracked. Cracks are usually caused 

 by defective shoeing or by excessive dryness. 



Sidebones are the ossifications resulting from inflamed 

 lateral cartilages. These cartilages help receive and distribute 

 the shock of impact. Inflammation causes bony deposits to 

 replace the cartilaginous tissue. These deposits often grow to 

 be noticeably large. 



Navicular disease is the result of an injury to the navic- 

 ular-bone or to its coverings or attachments that either fractures 

 the bone or sets up destructive inflammation in it. 



The navicular-bone is a little roller-shaped bone, lying in 

 the posterior angle between the lower pastern-bone and the 

 coffin-bone. The perforans tendon is fastened to the under side 

 of the coffin-bone. It bends over the navicular-bone, passes 

 behind the pastern, and, bending again over the sesamoids, 

 goes upward to its muscular development above the knee. 



This tendon transmits much of the shock of impact. The 

 navicular-bone, pinched in between it and the other bones of 

 the foot, is subjected to tremendous pressure at every stride. 

 Its surface must be smooth and well lubricated in order that the 

 tendon perforans may slip smoothly over it, in response to the 

 action of the muscles controlling it. If the pressure of the 

 tendon is too great for the health of the bone, it breaks, or 

 its envelope becomes inflamed and its structure changes. Its 

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