32 STRUCTURE AND ECONOMY OF THE HORSE. 



carpal bones is placed at the back of the knee, where It sustalng 

 no weight, but acts as a lever for the attachment of muscles, and 

 forms that prominence so perceptible at the back of the knee in 

 horses. x\lthough the knee does not possess so much motion as 

 tlie wrist in man, yet the horse requires a certain number of 

 bones and joints, in order to obviate the concussion to which he 

 would be otherwise liable ; for it is necessary that he should move 

 with great celerity, and, at the same time, that the vital organs 

 should be secured from the shock that would be experienced if 

 the same concnssion that the feet received were communicated 

 to the internal organs. To accomplish this purpose the joints 

 greatly contribute ; and none more so than that of the knee, 

 Avhich is placed at an equal distance between the body and the 

 ground. 



To neutralise the jar, no two bones are permitted to touch 

 each other, for each is tipped with cartilage at the place of 

 junction, and is covered with a fine delicate membrane, by which 

 an albuminous fluid, called synovia, is secreted. This fluid, being 

 confined by what is called the capsular ligament, lubricates the 

 joint, takes away the jar, and prevents the bones from coming 

 into contact with each other. The Importance of this fluid is 

 strikingly shown In cases where the joint Is opened by some 

 severe injury, and, the synovia escaping, the atmosphere Is 

 admitted ; the synovial membranes come in contact, and the 

 most severe Inflammation Is set up, attended with excessive 

 pain ; and the result frequently is, unless the cavity can be 

 quickly closed, the horse either dies from irritation, or the motion 

 of the joint Is destroyed by the secretion of bony substance in 

 and around it. 



The lower row of the knee bones rests upon the metacarpus ; 

 which in man and many animals Is composed of four bones, 

 nearly equal In size, but in the horse consists of one large and 

 two small metacarpal bones. The large one Is commonly termed 

 the cannon, and forms the principal bulk of the shank, being a 

 strong cylindrical bone, often a foot in length, reaching from 

 the knee to the fetlock joint. Like other cylindrical bones, the 

 cannon is smaller In the middle and larger towards the extre- 

 mities. The small metacarpal, or splint bones, although they 

 form a portion of the knee joint, yet do not reach more than 

 three-fourths of the length of the shank. They are attached to 

 the cannon by elastic ligamentous substance, and gradually taper 

 downwards, and end In bulbous extremities. With age they 

 become consolidated with the cannon, and In many horses a 

 bony substance, called a splint, unites them even in youth. 



The length of the metacarpus corresponds Inversely with that 

 of the humerus, and in proportion as the former is long and the 

 latter is short, and vice versa. Thus in man the humerus is 



