68 FORM AND ACTION. 



that concussion which otherwise must necessarily result from its 

 great action and speed : some of the weight or pressure which, 

 otherwise, must all have been received in a direct line by the 

 cannon bone, and from it have descended to the pastern, is now 

 diverted for the purpose of setting these springs in operation, and 

 thereby conferring elasticity and ease on the animal's move- 

 ments. 



Such has been the use ascribed by veterinary physiologists to 

 these bones, and no question that I know of has been raised about 

 its propriety, before Sir Charles Bell took it into consideration, and 

 expressed his dissent from it. " I have some hesitation," says 

 Sir Charles, in his Treatise on ' The Hand,' " in admitting the 

 correctness of the opinion of veterinary surgeons on this curious 

 piece of mechanism. They imagine that these moveable splint 

 bones, by plajdng up and down, as the foot is alternately raised 

 and pressed to the ground, bestow elasticity, and prevent concus- 

 sion. The fact certainly is, that by over-action this part becomes 

 inflamed, and the extremities preternaturally joined by bone to the 

 greater metacarpal or cannon bone ; and that this, which is called 

 a splint, is a cause of lameness." 



" I suspect, rather," continues Sir Charles, " that, in a perfect 

 state of the joint, these lesser metacarpal bones act as a spring to 

 throw out the foot when it is raised, and the knee bent. If we 

 admit that it is the quickness in the extension' of this joint on 

 which the rate of motion must principally depend, it will not escape 

 observation, that, in the bent position of the knee, the extensor 

 tendons have very little power, from their running so near to the 

 centre of motion of the joint ; and that, in fact, they require some 

 additional means to aid the extension of the leg." 



" Supposing that the head of the lesser metacarpal bone," says 

 Sir Charles, in explanation of the above, " enters into the compo- 

 sition of the joint, it does not appear that, by its yielding when the 

 foot is upon the ground, the bones of the carpus can descend, as 

 long as they are sustained by the greater metacarpal or cannon 

 bone ; I do not, therefore, conceive that this bone can add to the 

 elasticity of the foot. But when we perceive that the head of the 

 splint bone is behind the centre of motion in the joint, it is obvious 

 that it must be more pressed upon in the bent position of the joint 



