252 THE ARM. 



every rider. The lines above represent, in the order from the 

 front, the principal nerves, arteries, and veins of the shoulder 

 and arm ; and, on the muscles, k represents the principal sub- 

 cutaneous vein of the inside of the arm, and i the artery by 

 which it is accompanied. 



THE HUMERUS, OR LOWER BONE OF THE SHOULDER. 



Forming a joint with the shoulder-blade, at the point of the 

 shoulder, is the liumerus. It is a short, strong bone, slanting 

 backward in an opposite direction to the shoulder-blade. At the 

 upper part it has a large round head, received into the shallow 

 cavity of the shoulder-blade. In a well-formed horse this bone 

 can scarcely be too short. 



THE ARM. 



The ann extending from the elbow to the knee (see K and L, 

 Fig. 1, and also Fig. 35), consists, in the young horse, of two dis- 

 tinct bones. The long and front bone, called the radius, is nearly 

 straight, receiving into its upper end the lower heads of the hu- 

 merus ; and the lower end corresponding with the upper layer of 

 the bones of the knee. The short and hinder bone is called the 

 ulna. It has a very long and powerful projection, received be- 

 tween the heads of the humerus, and called the elbow ; it then 

 stretches down, narrowing by degrees (see L, Fig. 1, and the Fig. 

 35), to below the middle of the front bone, where it terminates 

 in a point. The two bones are united together by cartilage and 

 ligament ; but these are by degrees absorbed and changed to bone, 

 and before the horse becomes old the whole of the arm consists 

 of one bone only. 



The strength of the horse, so far as his fore limbs are concerned, 

 resides principally in those muscles which give size to the arm. 



A full and swelling fore-arm is the characteristic of every 

 thorough-bred horse. Whatever other good points the animal 

 may possess, if the arm is narrow in front and near the shoulder, 

 flat on the side, and altogether deficient in muscular appearance, 

 that horse is radically defective. He can neither raise his knee 

 for rapid action, nor throw his legs suflRciently forward. 



The arm should likewise be long. In proportion to the length 

 of the muscle is the degree of contraction of which it is capable ; 

 and in proportion also to the degree of contraction will be the 

 extent of motion in the limb beneath. 



Enlargements sometimes 'appear about the elbow, either the 

 consequence of a violent blow, or from the calks of the shoes in- 

 juring this part when the horse sleeps with his legs doubled under 

 him. If a seton is passed through the tumor, it will sometiniei» 



