2-62 DISEASES OF BONE. 



metacarpal bones), wLicli are separate during the early life of 

 the foetus, but become united before birth. Therefore although 

 the ox cannot now get a splint between his third and fourth 

 metacarpal or metatarsal bones, his ancestors at one period were 

 liable to this disease, from which the horse of the future will no 

 doubt be free. 



When the ancestors of the horse were three-toed animals, their 

 second and fourth metacarpal bones, which to-day are the splint 

 bones of the horse, served the useful purpose of forming joints 

 with their respective digits. But as these digits have disappeared, 

 the lower portion of the splint bones is no longer useful, and, 

 besides, is often a cause of lameness, on account of its presence 

 giving rise to a splint, or to irritation. The upper portion of 

 the splint bones forms joints respectively with certain small bones 

 of the knee or hock, as the case may be. It is impossible to say 

 with certainty how much of the splint bones of the horse is a useless 

 and undesirable appendage ; but tp judge by the size of similar 

 bones in the ox and sheep, it would probably be an advantage 

 to the horse if the lower two-thirds of his splint bones were non- 

 existent. Agreeably to principles already discussed, the closeness 

 of connection between a splint bone and its cannon bone decreases 

 from the knee (or hock) downwards. In fact, although the upper 

 end of a. splint bone is closely united to the head of its cannon 

 bone, its lower end is generally free. 



The foregoing observations tend to show that partial union of 

 a splint bone with its cannon bone is often a perfectly natural 

 result of increasing years, and cannot, in such a case, be regarded 

 as a disease. 



In the course of the evolution of the horse, the second and 

 fourth metacarpal bones, instead of occupying a more or less 

 forward position, as they once did, have gradually taken up their 

 positions at the back of their respective cannon bones ; the three 

 bones thus forming a groove for the suspensory ligament, which 

 was once a muscle. This arrangement of the splint bones is a 

 serious predisposing cause of lameness in horses ; because a splint, 

 on account of the consequent bony enlargement, would be apt to 

 give rise to painful pressure on this ligament. Hence the advis- 

 ability, when practicable, of removing the cause of lameness, 

 namely, the offending portion of bone. 



The distance of the lower end of a splint bone from its fetlock 

 is a very variable quantity; in fact, the splint bone, on rare 

 occasions, comes down to the level of the fetlock, and is furnished 

 with a pastern and hoof. In " Points of the Horse," I have given 

 a photograph I took of an example of this form of atavism. 

 Although the average curtailment of length of the splint bones 



