TYPES AND MARKET CLASSES OF LIVE STOCK 



349 



Muscular system. The horse comprises a great number 

 of systems of levers represented in the bones and joints, each 

 supplied with a system of muscles which furnish the power. 

 Muscles exert a force in only one way, and that by shortening, 

 giving a pull. For this reason muscles are arranged in pairs, 

 as illustrated by the biceps and triceps which move the fore- 

 arm in man. The flexor muscles are always inside the joint 

 and the extensors outside. The theory has been advanced 

 that the shortening of muscles is due to a change in the form 

 of the muscular cell from an elongated form to one nearly round 



Fig. 108. Skeleton of the Horse. 



This illustration shows the location of the bones and the degree to which 

 the skeleton and the muscle influence the form. 



when stimulated by nerve action. Muscles act through very 

 short distances and upon the short end of levers composing 

 the animal frame. Acting in this way, speed and distance are 

 gained with a corresponding reduction in the magnitude of the 

 force. Because muscles are able to act only through very 

 short distances, it is necessary for them to act upon the short 

 end of the levers in order that sufficiently rapid movement may 

 be gained. 



