816 DISEASES AND THEIE TKEATMENT. 



ure of the bone, represented by Fig. 720, happened near to the 

 point of the lever, while being raised, under weight from behind, 

 upon the point. In the case under consideration the bone had be- 

 come weakest on its inner half, precisely at the center line of the 

 foot, so depressed by its thinness that the foot tilted inward, and 

 gave way immediately beneath the pivot, the mid-line of the coro- 

 nary bone; this was also the fulcrum of the lever, the front of the 

 bone being its point of resistance. As in the former case, the rais- 

 ing of the foot from a plane toward a vertical line fractured the 

 corresponding bone in the two cases in different positions, but 

 through the same causes, weakened hoof, and the other adverse 

 conditions which led to atrophy of the bones. 



Fig. 722 is a representation of a fractured navicular bone, a 

 casualty of more frequent occurrence to horses in this country than 



FIG. 722. 



is commonly known, but which has scarcely been noticed. Fract- 

 ures of this kind are effects due entirely to long-protracted ad- 

 verse conditions of the feet, such as have been already dwelt upon. 

 I have never met with a case of fracture of either coffin or navicular 

 bone where previous long-prevailing diseased action of the foot was 

 not manifest. 



In the instance represented above, the reader may see that the 

 bone was extensively ulcerated and excavated like a decayed tooth, 

 and at last the fracture occurred in two lines diverging from the 

 excavated center to the anterior margin of the bone, where it is 

 connected to the coffin-bone. But I must request the reader to go 

 back with me to see the order and sequence of occurrence; the ex- 

 cavation of the navicular bone is a secondary occurrence, an effect 

 due to preceding and continuous deviations from health. 



The coffin-bone in Fig. 722 is wasted down to about two-thirds 

 of its natural depth and substance. Its semi-lunar crest is gone; 

 there is no sufficient concavity behind the plantar surface of the 



