ACTION OF MUSCLES OF NECK. 23 



but can also diminish the animal's speed, as I shall now 

 attempt to show. The shoulder of the horse, on each side 

 of the body, is connected by muscles to the trunk, on which 

 it can be moved backwards and forwards. The chief muscle 

 which draws the fore leg forward, is at one end attached to 

 the kumerus (the bone which is between the shoulder blade 

 and the fore-arm), and at the other end to the top of the 

 head. Consequently, a line passing through these two points 

 of attachment will be the direction in which the pull of 

 this muscle works. Therefore, when a horse holds his head 

 in the air, his front action will be necessarily high. All 

 muscles act by contracting, which the muscle that is attached 

 to the humerus and the head does, while keeping one of 

 its attachments fixed and the other movable. Hence, it can 

 draw the fore leg forward, when the position of the head 

 is kept fixed by other muscles of the neck. If the position 

 of the fore leg be fixed, as when the horse is standing still, 

 this muscle when stimulated will draw in the head and bend 

 the neck. Also, the farther the attachments of the respective 

 ends of a muscle are apart, the greater will be the distance 

 through which the pull of the muscle will act. Supposing, 

 therefore, that the muscle we are considering is 39 inches 

 long, and that it can contract to two-thirds of its ordinary 

 length ; it can exert a pull on its fore leg of 13 inches in 

 length, when it is on full stretch, by the fact of its attach- 

 ments being at their maximum distance apart ; that is to 

 say, when the neck is held straight and advanced. If, on 

 the contrary, the neck be bent, so that the attachments of 

 the muscle are 30 inches apart, the muscle will have a pull 

 of only 4 (13 9) inches. If the distance between the 

 attachments be 26 inches or less, the muscle will be thrown 

 out of action for the time being. We therefore see that by 

 altering the carriage of a horse's head and neck, we can 

 appreciably shorten his stride. 



