226 THE ARTICULATIOyS 



7/iajor joins the cai).<ule In-low. Internally are the long tendon of the biceps and the 

 gleno-hunieral ligament. 



The arterialsupply is derived from the siqjrascapular. anterior and posterior 

 circumflex, subscapular, dorsalis scapuhe, and a branch from the second portion of 

 the axillary artery. 



The nerve-supply is derived from the suprascapular, by branches in both fosste; 

 and from the circumlicx and subscapular nerves. 



The movements of the shoulder-joint consist of flexion, extension, adduction 

 and al)durtii)ii. rotation and circumduction. 



Flexion is the SAvinging forwards, extension the swinging backwards, of tlie 

 humerus; alxluction is the raising of the arm from, and adduction depression of 

 the arm to, the side. In flexion and extension the head of the humerus moves 

 upon the centre of the glenoid fossa round an oljlique line corresponding to the 

 axis of the head and neck of the humerus, flexion being more free than extension, 

 and in extreme flexion the scapula follows the head of the humerus, so as to keep 

 the articular surfaces in apposition. In extension the scapula moves much less, if 

 at all. 



In abduction and adduction the scapula is fixed, and the humerus rolls up and 

 down upon the glenoid fossa; during abduction the head descends until it projects 

 l)eyond the lower edge of the glenoid cavity, and the great tuberosity impinges 

 against the arch of the acromion; during adduction, the head of the humerus 

 ascends in its socket, the arm at length reaches the side, and the capsule is com- 

 l)letely relaxed. 



In circumduction, the humerus, by passing cpiickly through these movements, 

 describes a cone, whose apex is at the shoulder- joint, and the base at the distal 

 extremity of the bone or limb. 



Rcjtation takes place round a vertical axis drawn through the extremities of the 

 humerus from the centre of the head to the inner condyle; in rotation forwards 

 (that is, inwards) the head of the bone rolls back in the socket as the great tuber- 

 osity and shaft are turned forwards; in rotation backwards (that is, outAvards) the 

 head of the bone glides forwards, and the tuberosity and shaft of the humerus are 

 turned liackAvards, i.e. outAA'ards. 



Great freedom of movement is permitted at the shoulder, and this is increased 

 by the mobility of the scapula. Restraint is scarcely exercised at all upon the 

 movements of the shoulder by the ligaments, but chiefly by the muscles of the 

 joint. 



In abduction, the loAver part of the capsule is somcAvhat, and in extreme abduc- 

 tion consideral)ly, tightened; and in rotation iuAvards and outAvards, the upper part 

 of the capsule is made tense, as is also, in the latter movement, the coraco-humeral 

 ligament. 



The movements of abduction and extension have a most decided and definite 

 resistance offered to them other than by muscles and ligaments, for the great 

 tuberosity of the humerus, by striking against the acromion process and coraco- 

 acromial ligament, stops short any further advance of the bone in these directions, 

 and thus abduction ceases altogether as soon as the arm is raised to a right angle 

 Avith the trunk, and extension shortly after the humerus passes the line of the 

 trunk. 



Further elevation of the arm beyond the right angle is effected by the rotation 

 of the scajjula round its OAvn axis by the action of the trapezius and serratus 

 magnus muscles upon the sterno-clavicular and acromio-clavicular joints. 



The acromion and coracoid processes, together Avith the coraco-acromial liga- 

 ment, form an arch. Avhich is separated by a bursa and the tendon of the mpra- 

 .^pimtUis from the capsule of the shoulder. Beneath this arch the movements of the 

 joint take ])lace, and against it the head and tuberosities are pressed Avhen the 

 Aveight of the trunk is supported by the arms; the greater tuberosity and the upper 

 ]Kirt of the shaft impinge upon it Avhen abduction and extension are carried to their 

 fullest extent. 



No description of tlic sliouldcr-joint Avould be complete without a short notice 

 of the peculiar relation Avhich the biceps tendon bears to the joint. It passes over 

 the head of the humerus a little to the inner side of its summit, and lies free 



