MOTIONS OF THE SHOULDER JOINT. 205 



turned inwards or outwards, and in most persons extends to 

 three-fourths or even an entire circle. This motion concurs in 

 the action which brings the hand to the mouth, in consequence 

 of which such an action is performed with difficulty when the 

 clavicle is broken. After an accident of the kind, the head, in- 

 stead of remaining stationary as usual, is advanced towards the 

 hand, without which the act cannot be accomplished. A cer- 

 tain length in the clavicle seems indispensable to the vigorous 

 and perfect action of the shoulder in particular movements; if 

 the clavicle be disproportionately long, as in females, these 

 movements are executed with inevitable awkwardness and im- 

 becility; as, for example, in throwing a stone. 



The scapula presents a moveable basis, on which the mo- 

 tions of the arm are accomplished. Its primary motions are 

 such as have been assigned to the clavicle, in consequence of 

 the connexion between these bones; besides which, in all the 

 extreme motions of the humerus, backwards or forwards, the 

 scapula is caused to perform a partial rotation, the axis of 

 which is indicated by a line drawn from the end of the acro- 

 mion to the inferior angle. When the arm is brought very far 

 forwards, the inferior angle of the scapula is carried outwards, 

 and somewhat elevated, while the superior angle is directed 

 towards the spine, and somewhat depressed. But, when the 

 arm is carried very far backwards, the inferior angle is direct- 

 ed towards the spine, and the superior angle looks forwards 

 and upwards. The clavicle in these cases moves inconsidera- 

 bly, as the scapula enjoys a pendulous motion, and its point of 

 suspension is the outer end of the clavicle; at which place the 

 oblong articular surfaces slide laterally upon each other and 

 decussate. The extreme degrees of these motions tend to dis- 

 locate this articulation, but the accident is prevented by the 

 strong coraco-clavicular ligament, which, by its peculiar posi- 

 tion and conformation, resists firmly at a certain point. In the 

 abduction and adduction of the arm the scapula is motionless. 



SECT. VIII. OF THE MOTIONS OF THE SHOULDER JOINT. 



The os humeri is susceptible of elevation, depression, ad- 

 vancing, retreating, circumduction, and rotation. 

 VOL I. 18 



