CHAPTER XVII. 



THE LOCOMOTOR APPARATUS. 



The muscles are attached to bones, which form by their 

 movements on each other angles of varying size. These 

 angles are opened and closed during progression, and the 

 mechanical aid which is introduced to effect this is that of 

 the lever. 



The lever is composed of a power, fulcrum, and weight, 

 and, according to the relative position which these occupy, 

 we have formed a lever of the first, second, and third 

 order. 



In a lever of the first order the power is at one end, the 

 weight at the other, and the fulcrum between the two. If 

 we try to move a heavy box by placing a crowbar beneath 

 it, and a block under the crowbar, we are employing a 

 lever of the first order, the box beiDg the weight, the 

 block the fulcrum, and the hand of the operator through 

 the crowbar the power. The muscles which extend the 

 head act also as a lever of this order, the head being the 

 weight, the occipito-atloid articulation the fulcrum, and the 

 muscles of the neck the power. When the angle formed 

 between the scapula and humerus is reduced, the triceps 

 forms a lever of the first order, the muscle being the power, 

 the elbow the fulcrum, and the limb below the weight. In 

 extension of the hind-leg the gastroc muscles are the power, 

 the hock-joint the fulcrum, and the leg below the hock the 

 weight. 



This is principally a lever of extension, and exists all <>\ Ti- 

 the body. It is a lever of power, lor if the long-arm be 



