192 SURGICAL APPLIED ANATOMY. [Chap. xi. 



position may also be due to the rigid contraction of 

 the muscles about the joint that is usually observed. 

 When such contractions exist it may be inferred that 

 the powerful latissimus dorsi has a little advantage 

 over its opponents, and may be answerable for the rota- 

 tion in and slight projection backwards of the arm. 



There may be three diverticula from the synovial 

 membrane: (1) One that runs some way down the 

 bicipital groove with the tendon ; (2) a cul-de-sac 

 beneath the subscapularis, formed by a communication 

 between the synovial cavity and the bursa under that 

 muscle ; and (3) a cul-de-sac of like nature beneath 

 the infraspinatus muscle. The first-named is constant ; 

 the second is frequently present ; the third is rare. 

 When the joint is filled with effusion, the capsule is 

 evenly distended and the shoulder evenly rounded. 

 Special projections usually occur at the seats of the 

 diverticula. Thus a swelling often appears early in 

 the course of a synovitis in the groove between the 

 pectoralis major and the deltoid muscles, and this 

 swelling may appear bilobed, being cut in two by the 

 unyielding biceps tendon (Paulet). Fluctuation can 

 best be felt by examining the uncovered part of the 

 capsule in the axilla beyond the subscapular muscle. 

 When the joint suppurates pus usually escapes at one 

 of the cul-de-sacs just mentioned, most often through 

 the one that follows the biceps tendon. Pus may thus 

 extend for some way along the bicipital groove. Pus 

 escaping through the subscapular cul-de-sac is apt to 

 spread between the muscle and the venter of the 

 scapula, and to present at the lower and back part of 

 the axilla. Purulent collections beneath the deltoid 

 are nearly always conducted towards the anterior 

 aspect of the limb, being unable to proceed backwards 

 owing to the denseness of the fascia covering in the 

 deltoid and infraspinous muscles. In one recorded 

 case, pus that had escaped from the shoulder-joint 



