36 SKETCH OF THE ANATOMY OF THE HORSE. 



the point of the trapezium and the inside of the knee, so as to form a channel 

 for the " back tendons " to pass through. 



The sesamoid bones are fixed immovably to the back of the fetlock 

 joint. 



The fetlock, pastern, and coffin joints are hinge joints, which possess 

 more or less play. 



The hind Tunb is connected to the trunk, as we have already seen, by 

 the pelvis. 



The hip joint, formed by the head of the thigh bone and cavity in the 

 pelvis, is a ball and socket joint. 



In the stiUe we find two articulations — one with the thigh bone and tibia, 

 the other with the thigh bone and patella, which is firmly attached to the 

 tibia by ligaments in order to enable it to resist the action of those muscles 

 of the thigh which are inserted on it. 



The true hock joint is formed by the tibia and astragalus. It is a 

 hinge joint, which, owing to the oblique manner in which its grooves are 

 placed, causes the foot to be turned slightly outward when the joint is 

 either flexed or extended. The other joints of the hock possess hardly 

 any power of movement. 



The astragalus, os calcis, small bones of the hock, hind cannon, and splint 

 bones are firmly connected together by ligaments. 



The joints below the hock are similar to those below the knee. 



Muscles. — I shall now consider, in the briefest possible manner, 

 the principal muscles which are used in locomotion. 



A broad sheet of muscle {the pannictibis) lies immediately underneath 

 the skin that covers the neck, sides of the chest, and abdomen. In thin 

 horses, its rear border is usually defined by an irregular line {see pp. 256 

 and 257) which runs along the side downwards and backwards towards the 

 groin. This muscle is attached, round its borders, to the skin and 

 superficial muscles by sheets of fibrous tissue. By quickly contracting and 

 relaxing alternately, it causes the skin to twitch, and thus gets rid of flies, etc., 

 that may have alighted on the surface underneath which a portion of this 

 muscle lies. It is principally found on those parts which the horse has 

 difficulty in reaching with his lips, tail, or mane. As the process of training 

 for racing purposes appears to largely develop this muscle, I cannot help 

 thinking that it aids in forced expiration — expelling the air from the lungs — 

 during the quickened breathing entailed by fast work ; although anatomists 

 do not ascribe such action to it. 



