THE SHOULDER-JOINT. 



277 



arises internally at quite a distance from the glenoid cavity are probably due to a 

 very free opening into a large bursa. The tendon of the long head of the biceps 

 lies within the capsule from its origin at the top of the glenoid till it leaves the cap- 

 sule in the bicipital groove. The tendon does not lie free within the joint, but is 

 covered by a reflection of the synovial membrane as it lies curved over the head of 

 the humerus. On the young foetus it is attached to the inside of the capsule by a 

 synovial fold. The syniovial membrane of this joint is remarkably free from synovial 

 fringes. 



The bursae about the joint are numerous. The largest is the siibacromial or 

 subdeltoid bursa (Figs. 291, 292), situated between the top of the capsule, the 

 coraco-acromial ligament, and the acromion, and extending downward under the 

 deltoid. The subcoracoid bursa separates that process and the beginning of the 



Fig. 292. 



Clavicle 



Coraco-clavicular ligament 



Coracoid 



Capsule, 



Subdeltoid bun 



Deltoid muscle. 



process 



Glenoid 



ligament 



Glenoid 

 cavity 



Frontal frozen section through the right shoulder-joint. 



coraco-humeral ligament from the capsule. Other bursae are often found between 

 the capsule and the muscles inserted into the tuberosities ; that under the subseapu- 

 laris is constant. Of the others, the one most frequently found is under the infra- 

 spinatus ; it also may open into the joint. 



Movements. — When the arm is hanging close to the side adduction is almost 

 wanting, since, apart from the interference of the body, the humerus is arrested 

 at once by the lower border of the glenoid cavity. Backward movement is not 

 free, for the arm soon impinges on the overhanging acromion. Abduction has a 

 range of some 90° before the tenseness of the lower part of the capsule stops it. 



