MUSCLES OF SHOULDER 363 



the ulna and are inserted into the radius (supinator) , the thumb (abductor pollicis 

 longus, extensor pollicis longus and brevis) and index-finger (extensor indicis pro- 

 prius, fig. 369). All are supplied by the radial nerve. The chief function of the 

 brachio-radialis is to flex the forearm. The chief functions of the other muscles 

 are indicated by their names. 



The volar musculature (figs. 370, 371, 372, 375) arises from the medial side 

 of the lower end of the humerus and from the front of the radius and ulna and is 

 divisible into four planes. The muscles of the most superficial plane, pronator 

 teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris, arise from the 

 humerus and are inserted respectively into the radius, the radial side of the meta- 

 carpus, the palmar fascia and the ulnar side of the metacarpus. In the second 

 layer the flexor digitorum suhlimis arises from the humerus and the upper part of 

 the radius and ulna and sends tendons to the second row of phalanges of the fin- 

 gers. In the third layer the flexor digitorum profundus and flexor pollicis longus 

 arise from the radius and ulna and send tendons to the terminal row of phalanges. 

 In the fourth layer a single muscle, the pronator quadratus (fig. 377), extends in 

 the lower part of the forearm from the radius to the ulna. These muscles are 

 supplied mainly b}^ branches of the median nerve but the ulnar nerve supplies 

 the flexor carpi ulnaris and a part of the flexor profundus digitorum. The chief 

 functions of these muscles are indicated by their names. 



In the hand (figs. 368, 375, 376, 377, 379) there are several sets of intrinsic 

 muscles. About the metacarpal of the thumb is grouped a set of muscles which 

 arise from the carpus and metacarpus and are inserted into the metacarpal and 

 first phalanx of the thumb (flexor brevis pollicis, opponens pollicis, abductor pollicis 

 brevis, adductor pollicis). A similar set of muscles is grouped about the metacarpal 

 of the little finger (abductor digiti quinti, opponens digiti quinti, flexor brevis digiti 

 quinti) . These sets of muscles give rise respectively to the thenar and hypothenar 

 eminences. Between the metacarpals two sets of interosseous muscles arise; a 

 volar, adductor toward the middle finger and a dorsal, abductor group. They are 

 inserted into the sides of the bases of the first row of phalanges and into the 

 extensor tendons. They also flex the first row of phalanges and extend the other 

 two rows. From the tendons of the deep flexor muscle of the fingers, a series 

 of lumbrical muscles extends to the radial sides of the extensor tendons. They 

 flex the first row of phalanges and extend the other two. Over the thenar emi- 

 nence there is a subcutaneous muscle, the palmaris brevis. The muscles of the 

 hand are supplied by the ulnar nerve, with the exception of the two more radial 

 lumbricals and the abductor, opponens, and flexor brevis of the thumb, which are 

 supplied by the median nerve. 



Fasciae. — The muscle fascise of the upper extremities are well developed. The deltoid 

 and latissimus dorsi are contained in a fascial sheet which extends between them. The deeper 

 muscles which arise from the scapula are covered by strong fasciis. Of the pectoral muscles the 

 pectorahs major is covered by a delicate fascia, while the subclavius and pectoralis minor are 

 contained within the dense costo-coracoid membrane (fig. 358) which extends into the fascia 

 covering the axiUary fossa. The latter (fig. 359), is thin and is intimately fused to the tela 

 subcutanea. The muscles of the arm are enveloped in a cylindrical sheath which in the lower 

 half of the arm is united to the humerus by intermuscular septa. 



In the forearm near the wrist and on the back of the hand the tela subcutanea contains 

 httle fat. The antibrachial fascia forms a cyhndrical enclosure for the muscles of the forearm. 

 Near the wrist it becomes strengthened dorsally to form the dorsal ligament of the carpus 

 (posterior annular Hgament). This ligament converts the grooves on the back of the radius 

 into canals for the tendons of the extensors of the wrist and fingers. On the back of the hand 

 and fingers the fascia is intimately connected with these tendons. On the volar side near the 

 wrist the fascia is strengthened to form the volar ligament of the carpus. Beneath the ligament 

 lies the transverse ligament of the carpus which extends from the pisiform and hamate bones to 

 the tuberosities of the navicular and greater multangular bones. It completes an osteo-fibrous 

 canal for the tendons of the long flexors of the fingers. On the palm of the hand the fascia is 

 firmly bound to the bones by intermuscular septa, which separate the thenar and hypothenar 

 regions from a central palmar region. On the volar sides of the fingers the fascia forms the 

 vaginal hgaments of the flexor tendons. 



A. MUSCULATURE OF THE SHOULDER 



(Figs. 355, 356, 357, 363, 388) 



The muscles belonging to this group are the deltoid, the teres minor, the infra- 

 and supraspinatus, the latissimus dorsi, the teres major, and the subscapularis. 



