28 STRUCTURES OF THE BODY. 



hand to the shoulder, our brain telegraphs, so to speak, 

 the order, by means of the nerves, to the biceps muscle, 

 which is attached at one end to the shoulder-blade, close 

 to the shoulder-joint, and, at the other, to the bones of 

 the fore-arm, a little below the elbow. Hence this muscle, 

 on contracting, draws the hand up in the required 

 direction. 



As muscles are built up of contractile fibres, their 

 strength, other conditions being equal, is proportionate to 

 their thickness. 



In order to economise space, muscles are generally 

 attached to bones by means of tendons (sinews), which 

 are hard, fibrous cords of great toughness. In these 

 cases, the tendon at one extremity is united to the end 

 of the muscle ; and, at the other, to the bone. Tendon 

 is a changed form of muscle. "It is very difficult to 

 determine how the muscle and tendon are joined, or by 

 what means the union is brought about, for the parts 

 become insensibly blended " (Bland-Sutton). 



We find from experiment that a muscle can contract 

 to about two-thirds of its ordinary length, which is, there- 

 fore, proportionate to the extent of movement it is capable 

 of producing. If the muscles which move the hmbs 

 be comparatively short, the stride will also be short 

 and the horse will be slower than he would otherwise 

 be, no matter how thick and powerful are his muscles. 

 We may, therefore, conclude that speed is associated 

 with length of musclp, as has been stated in Chapter I. 



As length of muscle is necessarily accompanied by 

 length of bone, we may judge of the former by the latter, 

 which can usually be readily estimated. 



The " give and take " principle, which applies more 

 or less to all created things, holds good with muscles. 

 Hence, in the race-horse, for which the possession of 

 speed is the chief essential of success, we should seek 

 the greatest possible length of muscle, with just sufficient 

 strength to meet his requirements for carrying weight 



