MUSCLES Oi^ THE L\SIDE OF THE SHOULDER. 237 



MUSCLES 0^ THE INSIDE OF THE SHOULDER. 



PLATE VI. Fig. 2. 



a. Tlie flexor of the arm, -which is one of the most powerful of 

 the flexor muscles. It has its origin in the extremity of the 

 ridge of the shoulder-blade, in the form of a large and round 

 tendon, which extends between two prominences in the upper 

 portion of the front of the lower bone of the scapula. This 

 groove, or pulley, is as perfect as it is possible to suppose it ; 

 and is lined with smooth cartilage, between which and the 

 tendon there is interposed an oily fluid, which enables the 

 tendon to move in this pulley without the danger of being 

 injured by friction. Passing on from this pulley, and extend- 

 ing beyond the head of the lower bone of the shoulder, the 

 cord spreads out into a round fleshy substance, containing 

 numerous tendinous fibres. It is deeply seated, and gives that 

 fine fulness to the front of the arm. It is inserted into the head 

 and neck of the bone of the arm, as also into the capsular 

 ligament of the elbow-joint. It is the chief muscle, by which 

 nearly the entire of the leg below the arm is bent. 

 bj b. This muscle is called the pcctoralis transversus, or the muscle 

 which crosses the breast. It takes its rise from the first four 

 bones of the chest, and, stretching across to the inner part of 

 the arm, is inserted into the tendinous substance which covers 

 the muscles of the fore arm, and extending a considerable way 

 down the arm. Its use is to bind the arm to the side of the 

 horse, and it also keeps the legs straight before the horse when 

 it is at speed, so that the weight of the body may be received 

 on them in a direction most easy and safe to the horse as well 

 as the rider, and most advantageous for the full action of all 

 the muscles connected with progression. 



c. This represents the disease called capped hock, or an enlarge- 

 ment of the joint of the elbow, as described at page 131 



g. The internal flexor. It takes its rise from the inner head of 

 the lower bone of the shoulder, and is inserted into the head 

 of the inner splint-bone. Its ofiice is to bend the leg, and to 

 turn it very slightly. 



r. The principal veins, nerves, and arteries of the shoulder and arm. 



