■j:{S THE HORSE. 



of the foot. It therefure extends all these bones ; and as it passes over the 

 shank, being tied down to it in every part of its course, it likewise serves 

 lO extend that bone. 



At v., page 233, is the tendon of another extensor muscle, and at z a 

 curious oblique one, passing over the tendon of x, confining it in its situa- 

 tion, and likewise itself assisting in extending or straightening the leg. 



The muscles employed in bending the leg are both numerous and power 

 ful. Two of the superficial ones are given in the cut, page 233. The 

 first is at t, page 233 ; it is also seen at b, page 235. It is called the mid- 

 dle Jlexor, or bending muscle of the shank-bone, because it lies precisely 

 on the middle of the back part of the arm. It rises from the inner head 

 of the lower bone of the shoulder, and is inserted into one of the bones on 

 the inner side of the knee. The other is seen at v, page 233. It is called 

 the external flexor of the leg, because it lies on the outer side of the arm, 

 towards the back. It rises from the outer head of the lower bone of the 

 shoulder; advancing towards the knee, it is tendinous, and the tendon 

 divides into two portions, one of which is inserted into the same bone of the 

 knee, and the other into the outer small bone of the leg. The internal 

 flexor is seen at e, page 235. It proceeds from the inner head of the loAvei 

 bone of the shoulder, and is inserted into the head of the inner splint bone, 

 and its office is to bend the leg, and very slightly turn it. A portion of one 

 of the most powerful of the flexor muscles, and powerful indeed they 

 must be, is delineated at c, page 235. It is the Jlexor of the arm. It rises 

 from the extremity of the ridge of the shoulder-blade in the form of a large 

 and round tendon, which runs between the two prominences in the upper 

 part of the front of the lower bone of the shoulder, in as perfect a groove 

 or pulley as art ever contrived. This groove is lined witli smooth cartilage; 

 and between it and the tendon there is an oily fluid, so that the tendon plays 

 freely in the pulley without friction. Having escaped from this pulley, and 

 passed the head of the lower bone of the shoulder, the cord swells out into 

 a round fleshy body, still containing many tendinous fibres. Deeply seated, 

 it contributes materially to the bulk of the front of the arm ; and, 

 having reached the arm, it is inserted into the head and neck of the 

 bone of the arm, and likewise into the capsular ligament of the elbow- 

 joint. It is the main muscle by which, almost alone, the whole of the leg 

 below the arm is bent. 



It acts at great disadvantage. It is inserted into the very head of the 

 bone of the arm, and expanded even upon the joint. Then the power is 

 applied almost close to the centre of motion, while the weight to be raised 

 is fiir distant from it. The power is tiiirty times nearer the centre of 

 motion than is the weight ; and, calculating, as before, the weight of the 

 arm and the rest of the limb at tJO lbs., it must act with the force of thirty 

 times sixty, or 1800 lbs. In addition to this, the line of the direction of 

 the force strangely deviates from a perpendicular: the direction of the 

 muscle is nearly the same as that of the limb, and the mechanical disad- 

 vantage is almost incalculably great. We will take it at only ten times 

 more; then this muscle, and its feeble coadjutors, act with a force of ten 

 times 1800, or 18,000 lbs. 



Why this almost incredible expenditure of muscular power ? First, that 

 the beauty of the limb might be preserved, and the joint might be compact. 

 If tiie tendon had been inserted half way down the arm, the elbow-joint 

 would have offered a very unsightly appearance. 



Beauty of form, however, is the least result of this conformation ; with- 

 out it the animal would not have been fitted for the purposes to which wo 

 devote him. It is the law of mechanics, that what is lost in pc Aver is gained 



