32 CONFORMATION AND ITS DEFECTS 



These fleshy masses which clothe the bones are each and all endowed 

 with the property of contractility. When this power is called into action 

 by nervous stimulation it has the eiTect of bringing the two extremities of 

 the muscle towards each other, by which the length is diminished, while at 

 the same time its thickness increases. 



These changes are well seen in the biceps or muscle of the upper arm, if 

 the elbow be bent and the closed hand be brought up to the shoulder. 



When a stimulus is applied to a nerve entering a muscle, the latter is 

 made to contract throughout its entire length at nearly the same moment; 

 as a consequence, it is found that the period occupied by the contraction of 

 a short muscle is nearly equal to that required for a long one. It will be 

 obvious from this, that as a muscle will contract to the extent of one-third 

 of its length, the speed and propulsive power of a horse with long limbs 

 and long muscles will be much greater than that which can be produced by 

 another having short ones, assuming, of course, that all other things are 

 equal. 



Of two muscles of the same length whose activity of contraction is at 

 its raasiuium, the greatest power will be given out by that Avhich has the 

 greatest volume; in other words, the strength of a muscle is in proportion 

 to its thickness; and it is equally true to say that the longer the muscle the 

 greater will be the range of its contraction, and the more considerable the 

 displacement it will efiect in the movement of the bones to which it may be 

 attached. Hence it is that while muscles of strenoth are short and thick, 

 those of speed are long and slender. 



From the foregoing facts the conclusion may be drawn, that inasmuch 

 as short legs imply short muscles, animals so constructed must be compara- 

 tively slow in their movements however great may be their strength ; and, 

 conversely, horses whose legs are relatively long, and whose range of action 

 is necessarily more considerable, will be capable of developing a much 

 higher rate of speed. The draught-horse and the race-horse afford typical 

 examples of the truth of the proposition that " the volume of the muscles 

 gives the measure of force, their length that of speed ". In choosing the 

 one, therefore, the highest muscular develojniient consistent with reasonable 

 activity in the slower paces should be sought for, while in the other the 

 first and most important requirement is ample length of the leg muscles in 

 particular, combined with just so much thickness as will yield the necessary 

 power by which to support the weight and endure the strain that may be 

 imposed upon them. Any surplus muscle over and above these require- 

 ments will augment the weight, and tend rather to retard than to increase 

 the velocity of the gait. 



