BICEPS 307 



Flexdrs of the Forearm 



The flexor muscles are three in number. The most su])erfieial is the biceps, 

 which arises from th(^ sca])ula; while more clee])ly lie the brachialis anticus and 

 brachio-radialis (supinator longusj, which arise from the humerus. 



1. BICEPS 



The biceps flexor cubiti — named from its two heads and its action upon the 

 cul)itus, or elbow — is a thick, somewhat flattened fusiform muscle with a bifid upper 

 extremity. 



Origin. — (1) The short head from the outer side of the tip of the coracoid 

 ])rocess, in close connection with the coraco-l^rachialis muscle; (2) the long 

 head, from the upper border of the glenoid fossa of the scapula and from the 

 glenoid ligament. 



Insertion. — (1) The posterior border of the tubercle of the radius; (2) the 

 upi)er i)art of the deep fascia on the inner side of the front of the forearm, two 

 inches ( o cm. ) below the inner condyle of the humerus. 



Structure. — The short head arises by a short tendon from which the fleshy 

 fibres diverge in a somewhat conical form until they meet and Ijlend with the outer 

 and longer head about the middle of the ui)})er arm. 



The long head arises by a thick ribbon-like tendon three to four inches (about 

 9 cm. ) long, Avhich at its origin upon the upper liorder of the glenoid fossa bifur- 

 cates and blends with the glenoid ligament of the shoulder-joint. It first passes 

 outwards and arches over the rounded head of the humerus. It afterwards enters 

 the canal formed by the bicipital groove internally, and externally l^y the capsule 

 of the joint, together with the aponeurotic expansion derived from the tendon of 

 the pectoralis major. Down to this point it is invested by synovial membrane, 

 which is reflected upon it from the adjacent bone and capsule. After emerging at 

 the lower end of the bicipital groove it gives origin to a conical mass of fleshy fibres, 

 which meet with the fibres derived from the shorter head about the middle of the 

 up])er arm. The fleshy l^undles belonging to the two heads may be separated for 

 a considerable distance by careful dissection. A little below the middle of the 

 upper arm, the tendon of insertion commences as a septum between the two bellies 

 of the muscle. It rapidly increases in thickness, and about the level of the con- 

 dyles it becomes free, and as a flattened cord passes down in the middle of the 

 bend of the elbow and turns upon itself so that its anterior aspect now liecomes 

 external; before its insertion into the posterior liorder of the tuliercle of the radius 

 it is sei)arated from that process l)y a small synovial bursa. About an inch and a 

 half (4 cm. ) from its insertion it gives off from its inner ];)order a strong l)and of 

 fii)rous tissue three-quarters of an inch broad and one inch long (the semilunar 

 fascia), to the deep fascia covering the ulnar surface of the forearm. 



Nerve-supply. — From the outer cord of the brachial plexus (through the sixth 

 and seventh cervical nerves) by a branch of the musculo-cutaneous nerve which 

 enters the muscle on its posterior aspect near its inner border. 



Action. — (1) It flexes the elbow-joint by means of its radial insertion, and 

 also by the attachment of the semilunar fascia to the inner side of the forearm. 

 (2) It supinates strongly the forearm l)y means of the radial tendon which wra]is 

 round the tubercle of the radius. This movement will be most ])Owerful wlu'n the 

 ell)ow is l)ent to a right angle, as the tendon is then peri)endicular to the l)one, 

 which it causes to revolve. To increase its leverage, the tendon is lifted away from 

 the axis of the bone by the prominence of the tubercle. (3) It will assist some- 

 what feebly in the movements of the shoulder-joint, its short head being, like the 

 coraco-brachialis, a flexor and adductor of the upper arm. By its long head it 

 binds down the upper i)ortion of the humerus, and prevents the tendency to dislo- 

 cation u]iwards. "\Mien the forearm is fixed, the Ijiceps will help in flexing the 

 elbow, as in climbing or in drawing up the trunk to a horizontal bar. 



Relations. — Superficially, the deltoid and pectoralis major, the deep fascia. 



