THE HORSE IN MOTION 49 



The joints of the horse naturally are main factors in 

 locomotion. These may be grouped in two classes, mov- 

 able and immovable. The two ends of the bone are held to- 

 gether by strong, hard, fibrous tissues, known as ligaments. 

 There are several kinds of ligaments, some being white and 

 inelastic and others yellow and elastic. The normal pur- 

 pose of the inelastic ligament is to keep the end of the bone 

 within its socket. Some joints have considerable play, while 

 others are quite immovable. The ordinary ball and socket 

 joint, as seen in the shoulder or hip, is a striking example 

 of the movable joint. The more shallow the socket, the 

 more extensive the possible movement of the limb. Hinge 

 joints which possess motion in but two directions, forward 

 and backward, occur at various points, especially in 

 the elbow and hock. The knee has three hinge joints, one 

 of which, between the arm and cannon, allows much motion. 

 When the knee is bent, or the leg folds on itself, we say it is 

 flexed, and when straightened out, it is extended. 



The movements of the limbs and joints are made possi- 

 ble through the actions of levers, which are formed by the 

 bones and acted upon by the muscles, when stimulated by 

 the nerves. A lever is a rigid bar, either straight or curved, 

 which turns upon a fixed point, the fulcrum. At some point 

 on the lever is a weight, which may be moved by the appli- 

 cation of power at some other point. There are three 

 classes of levers. 



The lever of the first class is seen in using a long bar 

 as a pry. One end is placed under the object to be moved, 

 which is the weight, while the bar rests a short distance 

 from the weight on a point, the fulcrum. If power is ap- 

 plied at the long end of the lever, by bearing down, the 

 point beyond the fulcrum comes up with its weight. In 

 the case of the horse, a lever of the first class is seen in the 

 extension of the limbs, as for example when kicking back 

 with the hind foot. In this case the muscle pulls back 

 over the point of the hock, furnishing the power ; the ful- 



