30 SKETCH OF THE ANATOMY OF THE HORSE. 



The fetlocky pastern^ and coffin joints are hinge joints, which possess 

 more or less play. 



The hind limb 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 stifie 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 tnie 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 hones of the hock, hi?id cannon, and splint 

 hones 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 pajiniculus) 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 (p. 229) 

 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 lid 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 

 diflfiiculty 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 



The neck, back, and loins are flexed by muscles which lie immediately 

 underneath the spine. The head is bent by muscles that proceed — one on 

 each side — from the breast bone to the lower jaw, and by others which 

 copnect the neck and head together. The head is extended by muscles that 

 are attached to the poll and bones of the neck and by others that proceed 

 from the poll to the withers. The neck is extended by tlie last mentioned 

 muscles, and by those which connect the spine of one vetebra with the 

 body of the one in front of it. The back and loins are extended by muscles 

 which are similar in action to the one just alluded to, and by the longissimus 

 dorsi, which is the most powerful muscle of the body, and is the chief 

 extensor of the spine. It forms the principal portion of the fleshy mass 



