THE APvM. 239 



ill velocity. The product of the power, and the space passed over by the 

 arm of the lever to which it is attached, must always be equal to the pro- 

 duct of the weight, and of the space passed over by the arm that supports 

 it ; and if a power, equal to thirty times the weio-ht, is oblio-ed to be ex- 

 erted at the upper part of the bone of the arm, the centre of that bone, 

 which may be considered as the centre of the weight, will pass over thirty 

 times the space, and the extremity of the limb will pass over sixty times 

 the space. The muscle will contract with a great deal of rapidity, but the 

 foot will move with sixty times that rapidity, in order to pass over sixty 

 times the space in the same time. This is precisely what we want. Exten- 

 sive and rapid motion are the excellences of the horse. He is valuable in 

 proportion as he has them, combined with stoutness ; and by this con- 

 formation of the limb alone could he obtain them. Therefore the tendon 

 is at first unusually strong; it plays through the natural but perfect pulley 

 of the bone of the arm without friction ; the body of the muscle is mixed 

 with tendinous fibres, and the insertion into the fore-arm is very extensive, 

 lest the application of such immense force should tear it from its adhe- 

 sions. There is sufficient strength in the apparatus ; the power may be 

 safely applied at this mechanical disadvantage; and it is applied close 

 to tlie joint to give an extent and rapidity of motion which could not 

 otherwise have been obtained, and without which the horse would have 

 been comparatively useless. 



At the back of the arm are other flexor muscles of great power, to 

 bend the lower portions of the limb. We have described two of them 

 belonging to the arm and the leg, and we must not pass over the vei^y 

 peculiar ones acting on the feet. Only a small portion of one of them can 

 be seen in our cut, page 233, at 1. 



The first is the perforated flexor muscle : the reason of the name will 

 presently appear. It arises from the lower and back part of the inner head 

 of the lower bone of the shoulder, and intermixed with, or rather between 

 the origins of the muscle next to be described, and called the perforating 

 muscle. As it descends along the bone of the arm, it becomes tendinous; 

 and, approaching the knee, it is bound down by arches or bands of ligament, 

 that it may not start in sudden and violent action. Proceeding from the knee, 

 it widens, and partly wraps round the tendon of the perforating muscle, and 

 they run down together in contact, yet not adhering ; freely playing over 

 each other, and mucous fluid obviating all friction. Both of them are in- 

 closed in a sheath of dense cellular substance, attached to them by numerous 

 fibrils ; and they are likewise supported by various ligamentous expansions. 

 Near the fetlock the tendon still farther expands, and forms a complete ring 

 round the tendon of the perforating muscle. This is seen at J, p. 111. 

 The use of this will be best explained when we are treating of the fetlock. 

 The perforated tendon soon afterwards divides, and is inserted into the 

 smaller and larger pastern bones, and flexes or bends them. 



The next is the perforating flexor muscle. It has nearly the 

 same origin as the other, but with somewhat distinct heads. It con- 

 tinues muscular farther down the arm than the perforated, and lies 

 before it. At the knee it passes, like the perforated, under strong 

 ligamentary arches, which confine it in its situation. It then becomes 

 round, and is partly wrapped up in the perforated ; and at the fetlock is 

 entirely surrounded by it. It emerges from the perforated when that 

 tendon divides, and continues its progress alone after the other has inserted 

 itself into the pasterns, and, passing over the navicular bone, terminates on 

 the base of the coffin-bone, or bone of the foot. 



It is sufficiently plain that the arm should be large and muscular, 



