MYOLOGY 61 



B. MUSCLES OF THE UPPER ARM 



The muscles of the upper arm or brachium consist of 

 flexors and extensors. Of flexors there are three, namely 

 the 



Mm. biceps brachii 

 coracobrachialis 

 brachialis 



M. biceps brachii (figs. 6, 7, 13, 29) arises by two heads. 

 The longer has origin by a tendon from the bicipital process 

 upon the superior margin of the glenoid cavity and passes 

 craniad over the bicipital groove between the two tuberosi- 

 ties of the humerus. It is barely separable in Homodon- 

 tomys and Neotoma, but in Teonoma there are two rather 

 distinct divisions, the smaller slip lying upon the deep 

 belly, and being probably one-tenth the mass, of the larger. 



The short head arises from the coracoid process by the 

 tendon that is common to it and the coracobrachialis. It 

 does not join the long head until at the insertion, common to 

 both, which is by tendon onto the ulnar border of the radius 

 near its head. 



M. coracobrachialis (figs. 13, 29) is single in the present 

 genus. Origin is by the tendon common to this and the 

 short head of the biceps. It passes distad, mostly deep 

 to the latter muscle and craniad of the triceps medialis, 

 and is inserted along the medio-cranial border of the 

 humerus for its distal two-fifths, including the medial 

 epicondyloid ridge. 



M. brachialis (figs. 6, 13, 28, 29) arises by two heads. 

 The longer has origin from the lateral and caudal parts of 

 the neck of the humerus and a part of the greater tuberosity, 

 and passes distad along the lateral side of the deltoid ridge, 

 to be joined by the shorter head arising from the cranial 

 border of the shaft lying distad of the deltoid ridge. The 

 tendinous termination of the muscle, common to both 



