ELEMENTS OF HIPPOLOGY. 181 



m [CHAPTER XVI. 



ENDURANCE OF HORSES.— VICES.— PUNISHMENT. 



The endurance of a horse is the measure of his ability to 

 resist fatigue and is dependent directly upon his powers of di- 

 gestion and assimilation and the co-ordination of his nervous 

 and muscular systems. 



Muscular power is derived from the contraction of the 

 muscles. The muscles of locomotion are composed of numerous 

 fibers, built up in groups, and attached by a tendon at each end 

 to a bone. One of these bones serves as a fulcrum, the other as 

 a lever. The muscle lies between them. Each of the fibers of 

 the muscle, animated separately by a nerve, contracts, and the 

 whole muscle is shortened. The bones, when a flexor muscle is 

 contracted, are brought nearer together; they are separated more 

 when acted on by extensors. The muscular action is the same 

 in all muscles — the fibers contract in the direction of their length. 



As a muscle contracts its chemical nature changes. It con- 

 sumes oxygen and certain other elements brought to it by the 

 blood, which come to an active muscle in increased quantities, 

 and it gives off carbonic acid and numerous other waste products 

 that the blood washes off through the veins. 



The entire operation, the impulse given by the nerve, the 

 contraction of the muscle, and subsequent chemical change in 

 the constituent elements of the blood " feeding'- ' the muscle, 

 the pull on the tendon, and the resultant energy transmitted to 

 the bone, must work in perfect harmony with the corresponding 

 actions of all the muscles involved, and is consummated in an 

 almost inappreciable period of time. 



The muscles of locomotion are all voluntary muscles; all 

 are controlled by the volition of the animal. The muscles that 



