MUSCLES OF UPPER LIMB 361 



freedom of movement which permits their developing many important functions. 

 Primitively of value in climbing, in seizing food, preparing it for eating and 

 carrying it to the mouth, in attack and defense, their importance has been greatly 

 increased through the invention and use of tools, at first simple but constantly 

 increasing in complexity. They are also used as a means of social expression, as 

 seen primitively in the shrugging of the shoulders, or in the varied movements of 

 the arms which accompany heated discourse, and as finally developed in the art of 

 writing. In order to understand the muscles which are called into play in the 

 performance of these varied functions it is necessary to consider the various types 

 of movement which take place at each of the joints. Since, however, most 

 muscles act on more than one joint and the different parts of a muscle may act 

 differently on the same joint, it is convenient to take up the muscles of each 

 region of the limb in groups, based not so much upon the action of the muscles on 

 any one joint as upon the development of the group and the innervation of 

 the muscles composing it. 



Movement of the scapula is of essential importance in the movements of the arm. The 

 scapula is kept against the thorax by muscular attachments and atmospheric pressure, but it 

 may be moved forward, backward, upward, and downward, and may be rotated so that the 

 glenoid fossa, with which the head of the humerus articulates, is pointed forward when the arms 

 are carried forward, lateralward when the arms are abducted, upward when the arms are raised 

 high and somewhat downward when the arms are carried backward, thus greatly increasing the 

 extent of movement in these various directions. The acromio-clavicular, and sterno-clavicular 

 joints both allow hmited movements in various directions so that they resemble physiologically 

 limited ball and socket joints. The part played by the superficial and deep shoulder-girdle 

 muscles in the various movements has been described above, p. 356, in connection with these 

 groups of muscles. The action of these muscles is aided by the "pectoral muscles," (figs. 360, 

 388) and by the latissimus dorsi (fig. 355) described below. These muscles depress the scapula* 



At the humero-scapular or shoulder-joint the arm may be carried outward or abducted, 

 bodyward or adducted, forward or flexed and backward or extended. The last is much more 

 hmited in degree than the other two. The arm may also be partially rotated at this joint. 

 These various movements are brought about by the scapulo-humeral muscles (figs. 355, 356, 363) 

 and by the latissimus dorsi (fig. 355) and the pectoralis major, (fig. 360) assisted by the muscles 

 of the arm which arise from the scapula. They are produced in association with the movements 

 of the scapula described above. At the ulno-humeral joint the movements are relatively 

 simple, consisting of flexion and extension. Extension is produced at the elbow by the dorsal 

 muscles of the arm (fig. 363), flexion is produced not only by the ventral muscles of the arm, 

 which are inserted into the radius and ulna (fig. 364), but also by the more superficial of both 

 the main groups of muscles of the forearm. The pronation of the forearm, whereby the palm is 

 turned downward, and supination, whereby it is turned upward, take place in the joints be- 

 tween the radius and ulna at each extremity and between the radius and the lower end of the 

 humerus. At the upper radio-ulnar joint the radius is turned on its long axis, at the lower 

 joint it is carried about the lower end of the ulna. Pronation is produced chiefly by muscles 

 belonging to the ulno-volar group of forearm muscles (fig. 370); supination is produced by the 

 biceps of the arm (fig. 364) in conjunction with some of the muscles of the radio-dorsal group 

 of the forearm (fig. 367). At the wrist joints (radio-carpal, intercarpal), the movements are 

 those of flexion, extension, radial abduction and ulnar abduction. Volar flexion takes ])lace 

 chiefly at the radio-carpal joint, dorsal flexion at the intercarpal joint (Frohse). Extension 

 is produced by those muscles of the radio-dorsal group of the forearm, which send tendons 

 to the wrist and digits, flexion by the corresponding muscles of the ulno-volar group, radial 

 abduction is produced by the radial carpal extensors (fig. 367), and flexor ulnar abduction 

 by the ulnar carpal extensor and flexor (fig. 370). The varied movements of the thumb 

 and fingers, flexion, extension, abduction, and adduction are produced partly by muscles of 

 the two chief groups of forearm muscles, partly by the intrinsic muscles of the hand. Of 

 chief interest here are the free movements of the metacarpal of the thumb and the hmited 

 movements of the other metacarpals, that of the little fingers being the most movable, 

 as seen in spreading or cupping the hand. In flexion and extension of the metacarpal 

 of the thumb the movement is such as to bring the thumb into opposition to the fingers. In the 

 metacarpo-phalangeal joints those of the fingers admit of much greater freedom of movement, 

 flexion, extension, abduction, and adduction, than that of the thumb. The interphalangeal 

 joints are pure hinge joints and permit merely flexion and extension. 



Divisions. — The muscles described in this section as the muscles of the upper 

 limb are all differentiated from the blastema of the embryonic limb bud. Most 

 of them are differentiated in connection with the skeleton of the limb and extend 

 between the various bones which compose it, but a few grow out from the limb 

 bud over the trunk and become secondarily attached at one extremity to the 

 trunk, while the other extremity remains attached to the skeleton of the limb. 

 Thus the pectoral muscles (fig. 360), extend from the limb bud over the front of 

 the thorax and the latissimus dorsi extends over the side and back of the trunk 



* The upper sternal part of the pectorahs major, however, acting alone elevates the scapula, 

 and the glenoid fossa, the latissimus dorsi draws the scapula backward, the pectoral muscles 

 draw it forward. 



