190 SURGICAL APPLIED ANATOMY. [Chap. xi. 



from the anterior border of the acromion process. In 

 this posture, also, the head is wholly to the outer side 

 of the coracoid process. The margin of the glenoid 

 cavity is more prominent on the inner than on the 

 outer side, while the strongest part of the margin and 

 the broadest part of the fossa are below. This is sig- 

 nificant, since it points to an attempt to strengthen a 

 part of the joint that practice shows to be the weakest 

 in the articulation, viz., the lower and inner portion 

 of the capsule. It is at this place that the head of the 

 bone leaves the joint in dislocation of the shoulder. 



The capsule of the shoulder-joint is very lax, and 

 would lodge a bone-head twice as large as that of the 

 humerus. According to Henry Morris, no one part 

 of the capsule is constantly thicker than the rest, as is 

 the case in the hip-joint. The inner surface of the 

 capsule looks into the axilla, and is there free between 

 the two tuberosities, between the lesser one in front 

 and the posterior part of the greater process behind. 

 It is between these two projections that the humeral 

 head can be felt through the axilla. 



Of the Imrsse about the joint, the subacromial 

 bursa is the one most frequently the seat of disease, 

 and this sac, when distended with fluid, may be mis- 

 taken for the results of chronic inflammation, of the 

 joint (Fig. 18). 



Experiment shows that the walls of this bursa may 

 be actually torn in twists of the arm, especially when 

 either flexed or extended (Nancrede). When the sac 

 is distended most pain is elicited in the position of 

 abduction, for in this posture the bur sal walls are 

 normally folded up, so as to form a sort of collar in 

 advance of the greater tuberosity. When the walls 

 are thickened and distended by inflammation, abduc- 

 tion must press the bursa very forcibly under the 

 acromion, and so cause pain. In elderly people the 

 sac sometimes communicates with the joint. 



