FLEXORS OF THE ARM 379 



Insertion. — The tendon of insertion of the triceps forms a fiat band covering the dorsal 

 surface of the distal two-fifths of the muscle. It also extends proximally between the long and 

 lateral heads and on the deep surface of the former. This tendon is inserted into the olecranon 

 and laterally, by a prolongation over the anconeus, into the dorsal fascia of the forearm. 



Nerve-supply. — From the radial (musculo-spiral) nerve. The branch to the long head arises 

 in the arm-pit and enters that margin of the muscle which is prolonged down from the lateral 

 edge of the tendon, but which, because of the torsion of the muscle, comes to lie on the media! 

 side. The nerve usually enters through several rami about the middle of the free portion of the 

 long head. Somewhat "more distally the radial nerve gives oiT a branch that enters, by two or 

 three branches, the proximal portion of the medial head. A similar branch is given to the 

 lateral head and other branches are given to the lateral and medial heads from that portion of 

 the radial (musculo-spiral) nerve lying in the radial (musculo-spiral) groove. The nerve fibres 

 arise from the sixth, seventh, and eighth cervical nerves. 



Relations. — Near the shoulder the triceps is covered by the deltoid muscle. The long head 

 passes between the teres major and teres minor muscles. The circumflex (dorsal) scapular 

 vessels here pass medial, the circumflex humeral vessels and the axillary (circumflex) nerve 

 lateral, to this head. More distally the muscle lies beneath the brachial fascia. It covers the 

 radial groove of the humerus, in which run the radial (musculo-spiral) nerve and (superior) pro- 

 funda brachii artery. Ventro-lateral to the muscle lie the deltoid, brachialis, brachio-radialis, 

 and extensor carpi radialis muscles; ventro-medial, the coraco-brachialis, biceps, and brachialis 

 muscles. 



Action. — It extends the forearm. The leverage is of such a nature that force is sacrificed 

 for speed of movement. The long head of the triceps also serves to extend and to adduct the 

 arm and to hold the head of the humerus in the glenoid cavity. 



Variations. — The scapular attachment may extend for a considerable distance down the 

 axillary border of the scapula. Each of the heads may be more or less fused with neighbouring 

 muscles. Frequently a fourth head is found. This may arise from the humerus, from the 

 axillary margin of the scapula, from the capsule of the shoulder-joint, from the coracoid process, 

 or from the tendon of the latissimus dorsi. 



The latissimo-condyloideus (dorso-epitrochlearis). — This muscle is found in about 5 per 

 cent, of bodies. When well developed, it extends from the tendon of the latissimus dorsi to the 

 brachial fascia, the triceps muscle, the shaft of the humerus, the lateral epicondyle, the olec 

 ranon, or the fascia of the forearm. It is innervated by a branch of the radial (musculo-spiral) 

 nerve. It is a muscle normally present in some one of the forms above mentioned or in some 

 similar form, in a large number of the inferior mammals. In the human body it is normally 

 represented by a fascial slip from the tendon of the latissimus to the long head of the triceps or 

 the brachial fascia. 



The anconeus. — Origin. — By a short narrow tendon from the distal part of the back of the 

 lateral epicondyle and the adjacent part of the capsular ligament of the elbow-joint. 



Structure and insertion. — The tendon of origin is prolonged on the deep surface and lateral 

 border of the muscle. From this the fibre-bundles spread, the proximal transversely, the more 

 distal obliquely, to be inserted into the radial side of the olecranon and an adjacent impres- 

 sion on the shaft of the ulna. Its superior fibre-bundles are usually continuous with those of 

 the n edial head of the triceps. 



Nerve-supply. — By a long branch which arises in the radial (musculo-spiral) groove from the 

 radial (musculo-spiral) nerve, passes tlirough the medial head of the triceps, to which it gives 

 branches, and enters the proximal border of the anconeus. The nerve fibres arise from the 

 seventh and eighth cervical nerves. 



Action. — It aids the triceps in extending the forearm and draws the ulna laterally in prona- 

 tion of the hand. 



Relations. — The muscle lies immediately beneath the antibrachial fascia. It extends over 

 the head of the supinator (brevis) and the elbow-joint and upper radio-ulnar joint. 



Variations.— The extent of fusion of the muscle with the medial head of the triceps varies 

 a good deal. It may also be fused with the extensor carpi ulnaris. It has been reported 

 missing. 



B. intratendinea olecrani. — Within the tendon of the triceps near its insertion. More 

 frequent than the following: — • 



B. subtendinea olecrani. — Between the tendon of the triceps and the olecranon and dorsal 

 ligament of the elbow-joint. Inconstant. 



B. epicondyli medialis dorsalis. — Between the medial epicondyle, the edge of the triceps, 

 and the ulnar nerve. Rare. 



B. m. anconei. — Between the tendon of origin of the muscle and the head of the radius. 

 Frequent. 



2. Ventral or Flexor Group 



(Figs. 364, 365, 370, 372) 



The muscles of this group are the coraco-brachialis, the biceps, and the brachi- 

 alis. The coraco-brachialis (fig. 365) is a band-like muscle which arises from 

 the coracoid process and is inserted into the middle third of the shaft of the 

 humerus. The biceps (fig. 364) arises by two heads: a short head, closely as- 

 sociated with the coraco-brachialis, from the coracoid process; a long head, by an 



