THE HORSE IN MOTION. 49 



the drawing, being there confounded with the body of the muscle lying 

 upon it. On their way to their insertion into the point of the hock the 

 tendons of these two muscles are twisted upon each other half round, so 

 that the perforatus tendon, which was beneath, reaches its insertion at 

 the outside of that of the gastrocnemius. The tendon of the latter is 

 fixed immovably to the bone, and acts to extend the metatarsus below 

 it, but the tendon of the perforatus passes over the point of the hock, 

 where it is provided with a pulley similar to that at the knee, over 

 which it glides to a very limited extent, being strongly secured by liga- 

 ments to the point of the hock, h; it then passes down behind the 

 metatarsus, or cannon bone, to the pastern, or fetlock joint, where it 

 throws out a ring to encircle the tendon of the per/oraiis, as seen at 

 r. (These two tendons, forming the " back sinews," would be liable, 

 from the extreme flexions and extensions which take place at that 

 joint, to be dislocated, but for the extraordinary provisions made to 

 prevent it.) It then passes to its insertion into the bones of the foot. 

 When the knee is flexed, as in the plate, this tendon (perforatus), 

 being inserted into the femur above the knee joint, is relaxed, and the 

 extensors of the foot, which are located in front (<?), are permitted to 

 straighten or extend the foot, as may be seen in all the plates where 

 the hind foot is in the act of taking the ground ; but when the leg is 

 extended upon the thigh the tendon is drawn upward, and flexion at 

 the joints of the foot is effected, the extensors at a offering no oppo- 

 sition, so that extension of the superior joints, as in the act of propul- 

 sion, causes flexion of the inferior. This movement is independent 

 of muscular action, and may be shown in the dead subject, except so far 

 as the act of the extensor of the foot (extensor pedis, a), is concerned ; 

 but the spindle-form body of the perforatus muscle connected with the 

 tendon contracts by volition, and flexes the foot with its added force. 



If we consider the limb in the position as given in the plate, and 

 then forcibly extend the foot until the pastern joint, 6", is in the posi- 

 tion it takes Avhcn the horse is standing, the tendon, /, will become 

 tense, and also the ligaments that limit its motion at the point of the 

 hock, // ; beyond that it cannot be moved by any force that we can 

 apply short of breaking. It is tied by the ligaments at the apex of 



7 



