MUSCLES OF THE ARM. 419 



The Triceps Extensor Cubiti, or Brachii, 



Forms the whole of the fleshy mass on the back of the arm ; 

 it therefore occupies the space between the integuments and the 

 bone. It arises by three heads. The first, called Lorigus, 

 comes, by a flattened tendon, between the teres major and the 

 minor muscle, from a rough ridge on the inferior edge of the 

 cervix scapulas. The second, called the Brevis, arises by a sharp, 

 tendinous, and fleshy beginning, from a slight ridge on the outer 

 back part of the os humeri, just below its head. The third head, 

 called Brachialis Externus, arises, by an acute fleshy beginning, 

 from the inner side of the os humeri near the insertion of the 

 teres major. This muscle, both at its external and internal 

 edge, is separated from the muscles in front of the arm by the 

 external and internal inter-muscular ligaments, which arise near 

 the middle of the os humeri, and run to the condyles respec- 

 tively. The whole back of the os humeri, as well as the pos- 

 terior surface of these inter-muscular septa, is occupied by the 

 origin of the triceps. The muscular fibres run in various direc- 

 tions, according to their respective heads and places of origin. 



At the inferior end of the muscle is found a broad tendon, 

 which covers its posterior face. This tendon is inserted into 

 the base or back part of the olecranon, and the ridge leading 

 down the ulna on its radial side. The bellies of the triceps 

 unite above the middle of the os humeri, but the interstices be- 

 tween them may be observed much lower down. There is a 

 bursa between the tendon and the olecranon process ; besides 

 which, there is sometimes another on each side of the first. 



The triceps extends the fore arm. 



The Jlnconeus, 



Is a small triangular muscle, just beneath the skin, at the outer 

 posterior part of the elbow joint. It arises tendinous from the 

 posterior lower part of the external condyle of the os humeri, 

 adheres to the capsular ligament of the joint, and is partly co- 

 vered by the tendon of the triceps. 



It is inserted, fleshy and thin, into the ridge leading from the 



