The Arm. 51 



The action of the biceps, arising by its long head 

 from the same structure as the long head of the triceps, 

 viz., the cartilaginous rim of the glenoid fossa, and by 

 its short head from the apex of the coracoid process, and 

 inserted into the bicipital tuberosity of the radius, is 

 to flex the forearm. Continuing its action it flexes the 

 arm, and, on account of its insertion into the posterior 

 part of the bicipital tuberosity, it rotates the radius out- 

 wards, i.e. it supinates the hand. The expansion of fascia 

 given off from the inner border of the biceps tendon to 

 the fascia of the forearm brings the muscle into direct 

 connection with the fascia of the forearm, and, since some 

 of the flexor muscles arise from the under surface of the 

 deep fascia of the forearm, traction on this fascia by the 

 biceps would tend to induce a slight degree of tension of 

 these flexor muscles, consequently flexion of the forearm 

 by the biceps would be associated with, and the cause of, 

 a slight degree of flexion of the fingers, and one can 

 notice that flexion of the forearm is slightly easier with 

 the fingers flexed than when they are extended so that the 

 grasping power of the fingers is increased by the biceps 

 in such actions as climbing a pole, etc. 



The action of the coraco-brachialis has already been 

 considered, while the brachialis anticus, from the lower 

 half of the outer and inner surfaces of the humerus into 

 the coracoid process of the ulna, flexes the forearm. 

 These muscles are supplied by the musculo-cutaneous 

 nerve, the brachialis anticus receiving in addition a few 

 filaments from the musculo-spiral. 



In the case of the triceps, the actions of which have 

 already been considered, there is an expansion of fascia 

 given off from the outer side of its tendon to blend with 

 the fascia of the extensor aspect of the forearm, and since 

 this fascia gives origin to some of the extensor muscles, 



