8 May, 1907.] Lameness in Horses. 267 



when just put to work on hard ground. The existence of hereditary in- 

 fluence is an often-noticed and undisputed factor in the occurrence of 

 splints. Whether accompanied by lameness ox not the presence of splints 

 constitutes a technical unsoundness ; although, in a matured horse, if the\' 

 are not causing lameness and are so situated as not to be liable to interfere 

 with the action of tendons, the horse may be passed as actually sound. 



Development of Splin-ts. — Professor Williams' teaching was that a 

 splint is an hypertrophy or excessive growth of bone, at the particular 

 part where it occurs, promoted by the nature of the work performed to so 

 strengthen the part as to enable it to withstand the concussive shock inci- 

 dental to work on hard ground. In this way he explained the formation 

 of large splints without the occurrence of lameness. He also held that 

 lameness only occurs when the bone forming activity is exaggerated into an 

 actual inflammation of the bone or its covering (ostitis or peri-ostitis) or 

 when, after the splint has formed and the two bones are strengthened by 

 union, the bony enlargement is so situated as to interfere with the move- 

 ment of the flexor tendons or to press upon the nerve of the part. 



In view of a complete capitulation to Darwin's theory of evolution, 

 which the author confesses to, he is inclined to go further than Williams, 

 and to sav that splint formation is a perfectly natural process — as natural 

 under the conditions of horse life usually existing at the age period of 

 splints as is the ordinary development and hardening of bone, the develop- 

 ment and strengthening of muscle by work and training, or the growth of 

 coat on the approach of winter. In each of these latter cases the changes 

 occur as the result of surrounding circumstances which gradually induce 

 their requirement. Bones harden as they are called upon to withstand 

 shock and strain ; muscles strengthen as the work required of them in- 

 creases ; the coat grows as the necessity for protection from the weather 

 arises; and, pursuing the same line of reasoning, splints are formed in 

 response to the demand for that greater strength of the bones immediately 

 below the knee which is required to withstand the concussive shock asso- 

 ciated with present day conditions of horse-work. 



In support of this view that the formation of splints is largely an evo- 

 lution process, consideration of such facts as the following may be invited. 



The pre-historic horse, which existed at a time when the earth's crust 

 had not emerged from a condition of bogginess was, so far as can be 

 ascertained, a five-toed animal belonging to the species of which the tapir 

 and the rhinoceros are present-day representatives. As the surface of 

 the earth hardened, and the necessity for the expanding five-toed foot de- 

 creased, the evolution or metamorphosis into the soliped horse of our time 

 can be traced by means of fossil remains through the Eoliippus (Hipparion) 

 which had four toes and the Mesohip-pus which had three toes. It is by 

 no means unusual for horses to be born now-a-days which, by the possession 

 of one or more supernumerarv digits, manifest a reversion to one or other 

 of these original ancestors. (Fig. 11.) The fusion of the digits has been tak- 

 ing place gradually throughout thousands of generations until now there re- 

 mains but one complete digit, comprising a large metacarpal or cannon 

 bone {os metacarfi magnus) articulating at the fetlock joint with the lung 

 pastern bone, and two small metacarpal or splint bones {ossa metacarfi 

 farvi) one situated on the outer and the other on the inner aspect of the 

 large bone posteriorly. These small bones do not extend downwards as 

 far as the fetlock. They are the remains of previously existing outer and 

 inner complete digits. 



