MUSCLES SITUATED ON THE OS HUMERI. 



363 



forearm, and a number of the fibres, from opposite sides, 

 'decussate each other. It serves to strengthen the muscles, by 

 keeping them from swelling too much outwardly, when in 

 action ; and a number of their fleshy fibres take their origin 

 from it. 



2. Brachialis Interims, ."r fit* 



Arises, fleshy, from the middle of the os humeri, at each side 

 of the insertion of the deltoid muscle, covering all the inferior 

 and forepart of this bone, runs over the joint and adheres firmly 

 to the ligament. 



Fig. 93.* Inserted, by a strong tendon, into 



the coronoid process of the ulna. 



Use. To bend the forearm, and to 

 prevent the capsular ligament of the 

 joint from being pinched. 

 Behind, are 



1. Triceps Extensor Cubiti, 



Arises, by three heads ; the first call- 

 ed longus, somewhat broad and tendi- 

 nous, from the inferior costa of the 

 scapula, near its cervix. The second 

 head, called brevis, arises by an acute, 

 tendinous, and fleshy beginning, from 

 the back part of the os humeri, a little 

 below its head, outwardly. The third, 

 called brachiatis externus, arises by 

 an acute beginning, from the back part 

 of the os humeri. These three heads 

 unite lower than the insertion of the 

 teres major, and cover the whole posterior part of the humerus, 

 from which they receive addition in their descent. 



* A posterior view of the arm, showing the triceps extensor cubiti muscle. 

 1. Its external head called brevis. 2. Its long or scapular head. 3. Its inter- 

 nal head, called in contradistinction with a muscle on the front of the arm, 

 brachialis externus. 4. The olecranon process of the ulna. 5. The radius. 6. 

 The capsular ligament of the shoulder joint. 



