chap, xi.] THE SHOULDER-JOINT. 195 



the axilla, since the head, having left the glenoid fossa, 

 must occupy some part comprised within that cir- 

 cumference. Again, Dr. Dugas has pointed out that 

 " if the fingers of the injured limb can be placed by 

 the patient, or by the surgeon, upon the sound 

 shoulder while the elbow touches the thorax (a con- 

 dition that obtains in the normal condition of the 

 joint), there can be no dislocation ; and if this 

 cannot be done there must be one, for no other injury 

 than a dislocation can induce this physical impossi- 

 bility." This depends upon the fact that in con- 

 sequence of the rotundity of the thorax it is impossible 

 for both ends of the humerus to touch it at the same 

 time, and in luxation at the shoulder the upper end 

 of the bone is practically touching the trunk. Lastly, 

 from the position of the great vessels and nerves it 

 will be seen that in the subcoracoid and subglenoid 

 luxations the head of the bone may press injuriously 

 upon those structures. Thus may result oedema of 

 the limb from pressure on the veins, and severe pain 

 or loss of muscular power from pressure on the 

 nerves. The artery is usually saved by its greater 

 elasticity ; but Berard reports a case of displacement 

 forwards where the axillary artery was so compressed 

 by the humeral head as to induce gangrene of the 

 limb. 



The close connection of the circumflex nerve with 

 the humerus renders it very liable to injury, especi- 

 ally in the subglenoid and subspinous forms of dis- 

 location. 



Special anatomy of each form. 1. Sub- 

 coracoid. The articular head of the humerus lies on 

 the anterior surface of the neck of the scapula, and the 

 anatomical neck rests on the anterior lip of the glenoid 

 fossa. The head is thus placed immediately below the 

 coracoid process, and is in front of, internal to, and 

 a little below, its normal site. The great tuberosity 



