THE MUSCULAll SYSTEM. 39 



front part of the scapula, one of which Is attached to the 

 humerus, and the other to the radius. Another muscle is at- 

 tached to the humerus just below the shoulder joint, and to the 

 upper and outer part of the radius. Behind the shoulder joint, 

 and filling up in great measure the space formed by the scapula 

 and humerus, there is a very large muscular body, which is ex- 

 ceedingly prominent in many horses, particularly in thorough- 

 bred ones. It is this muscle which forms a principal part of a 

 shoulder of mutton. It is called the triceps extensor brachii ; 

 and, if we regard it as one, has three separate origins and one 

 insertion, namely, the ulna. One head rises from the posterior 

 ridge of the scapula ; another from the outer part of the 

 humerus; and the third head from the inner part of this bone. 

 Thus situated, it principally extends the arm. 



There is also another muscle in this situation attached above 

 to the humerus, and below to the point of the ulna and the 

 capsular ligament of the elbow joint. 



The muscles of the Arm and Fore-leg consist of the extensors 

 and the flexors, so denominated from their use being either to 

 extend or to bend the leg. The extensors are four in number, 

 and occupy the front of the arm, being very prominent in some 

 horses, particularly those who stand firm on their legs. One 

 of these muscles is attached to the lower part of the humerus, 

 and to the upper and front of the cannon bone. Another is 

 attached to both the humerus and ulna above, and below by 

 means of a long tendon which commences above the knee, to 

 the two pastern and the coffin bones. 



A third muscle is attached above to the radius and the ulna, 

 and below to the large pastern. 



The fourth, smaller than the others, is attached above to the 

 body of the radius, and below to the internal splint bone. 



The flexor muscles of the arm are eight in number, and are 

 divided into two regions, four being deep-seated, and four super- 

 ficial. Of the former, one is attached to the humerus above, 

 and below to the bone which projects behind the knee and to the 

 outer splint bone. Another rises from the humerus, and also 

 from the ulna, and is inserted, like the former, into the trape- 

 zium. Thus, there are two muscles which are inserted into 

 this small Lone behind the knee, which thus forms an important 

 lever, and should therefore be prominent and well developed. 



A third muscle in this region is attached above to the hu- 

 merus, and below to the internal splint bone, and the fourth is 

 attached to the ulna above, and joins the perforans tendon below. 

 The four muscles belonging to the deep-seated region are, of 

 course, situated in front of those just described. 



Two of them, called the Jiexor perforatiis and perforans, so 

 called because the tendon of the former is perforated by the 



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