362 THE MUSCULATURE 



as far as the iliac crest (fig. 355). The muscles of the limb may be divided into 

 two great divisions, a dorsal division, innervated by nerves arising from the back of 

 the brachial plexus (supra- and subscapular, axillary and radial nerves) and a 

 ventral division innervated by nerves arising from the front of the plexus (sub- 

 clavian, anterior thoracic, musculo-cutaneous, median and ulnar). The former, 

 which correspond with the musculature on the back of the shark's fin, are in the 

 main extensors; the latter, which correspond with the musculature on the front 

 of the shark's fin are in the main flexors. The bellies of the muscles of each 

 division are found in the region of the shoulder and thorax, the arm, the forearm, 

 and the hand. 



The shoulder muscles belong to the dorsal division. They arise from the 

 lateral third of the clavicle and from both surfaces of the scapula and are inserted 

 into the upper part of the humerus. They include the deltoid (fig. 355), the chief 

 abductor of the arm; the supraspinatus, the infraspinatus and the teres minor 

 (fig. 363), all lateral rotators; the suhscapularis (fig. 356), the chief medial rotator; 

 and the teres major (fig. 355), a medial rotator and adductor. With these may 

 be classed the latissimus dorsi (a medial rotator, adductor and extensor) (fig. 

 355), which arises from the dorsolumbar fascia and the crest of the ilium and is 

 inserted into the upper part of the shaft of the humerus. These muscles are sup- 

 plied by the suprascapular, the subscapular, and the axillary nerves. 



The pectoral group belongs to the ventral division. It includes the pedoralis 

 major (fig. 360), a powerful flexor and adductor of the arm arising from the anterior 

 chest wall and inserted into the shaft of the humerus; the pedoralis minor (fig. 

 388), which arises from the chest wall and is inserted into the coracoid process of 

 the scapula, and the subdavius (fig. 361), which extends from the first rib to the 

 clavicle. These muscles are supplied by the subclavian and the anterior thoracic 

 nerves. 



In the arm the dorsal division is represented by the triceps and anconeus, 

 (fig. 363). The triceps arises from the scapula and the back of the humerus and is 

 inserted into the olecranon process of the ulna. The anconeus arises from the 

 radial epicondyle of the humerus and is inserted into the olecranon process. Both 

 muscles extend the forearm. The triceps also adducts the arm. They are 

 supplied by the radial nerve. 



The ventral division is made up of the coraco-brachialis (fig. 365) ; the biceps 

 (fig. 364); and the brachialis (fig. 365). The coraco-brachialis (fig. 365), arises 

 from the tip of the coracoid process of the clavicle and is inserted into the shaft of 

 the humerus. It adducts and flexes the arm. The biceps (fig. 364), arises by a 

 short head from the coracoid process and by a long head from the scapula above 

 the glenoid fossa and is inserted into the radius and the fascia of the forearm. It 

 flexes and supinates the forearm. The long head is an abductor, the short head 

 an adductor and flexor of the arm. The brachialis (fig. 365), arises from the 

 lower part of the shaft of the humerus and is inserted into the ulna. It is a 

 flexor of the forearm. 



The two main divisions of the musculature of the forearm give rise to the 

 prominences on each side of the elbow-joint. Their peculiar arrangement with 

 respect to the humerus is because in man, as in most tetrapods, the normal posi- 

 tion of the forearm is one of pronation and in this position the back of the forearm 

 is in line with the radial epicondyle, the front with the ulnar epicondyle. The 

 dorsal or extensor muscles, springing from the lower end of the humerus (fig. 367), 

 get the most direct purchase when attached to the radial epicondyle, and the 

 ventral or flexor muscles (fig. 370), the most direct purchase when attached to the 

 ulnar epicondyle. The two divisions of the musculature may therefore here be 

 designated the radio-dorsal and the ulno-volar or volar divisions. The main 

 bulk of the musculature is found in the upper part of the forearm. At the wrist 

 num(!rous tendons pass over to th(! wrist, palm and digits. This arrangement 

 facilitates movement of the hand. 



The muscles of the dorsal division (figs. 367, 368, 369), are divisible into two 

 groups, a superficial and a deep group. Those of the superficial group arise 

 from the radial side of the lower (!nd of the humerus and are inserted into the dorsal 

 end of the radius (brachio-radialis) , the radial and ulnar sides of the metacarpus 

 {extensor carpi radialis longus and brevis and extensor carpi ulnaris) and into the 

 backs of the digits {extensorcs digitorum). The deeper muscles arise chiefly from 



