THE SHOULDEK-JOINT. 



321 



tissue attached to the margin of the glenoid cavity. Many of its fibres are 

 short, and pass obliquely, from the inner to the outer aspect of the ridge, so 

 that its attached base is ' broader than its free edge, and therefore in cross 

 section it appears somewhat triangular. The long tendon of the biceps, which 

 arises from the apex of the glenoid cavity, becomes to a considerable extent in- 

 corporated with the labrum glenoidale. 



Capsula Articularis. The fibrous stratum (O.T. capsular ligament) (Fig. 302) 

 of the articular capsule presents the general shape which is characteristic of the 

 corresponding part in other ball-and-socket joints, viz., a hollow cylinder. By its 

 proximal end the fibrous stratum is attached to the circumference of the glenoid 

 cavity, external to the labrum glenoidale, and also, to a considerable extent, to the 

 labrum glenoidale itself. 



By its distal end it is attached to the neck of the humerus, and therefore 

 beyond the articular area of the head. The fibrous stratum is strongest on its 

 superior aspect, while interiorly, where the neck of the bone is least defined, it 



Coraco-acromial ligament 



Acromion 



Communication 



between subscapular 



bursa and joint cavity 



Articular capsule 



Coraco-humeral 

 ligament 



Subscapularis 

 muscle 



11 



I Long 

 l-tendon 

 n of biceps 



FIG. 302. CAPSULE OF THE SHOULDER- JOINT AND CORACO-ACROMIAL LIGAMENT. 



extends distally for a short distance upon the humeral shaft. Its fibres for the most 

 part run longitudinally, but a certain number of them pursue a circular direction. 



The greater part of the epiphyseal line of the proximal end of the humerus is 

 extra-capsular, but it is intra-capsular on the medial side of the bone. 



A prolongation of the fibrous stratum, the transverse humeral ligament presenting 

 both longitudinal and transverse fibres, bridges that part of the intertubercular 

 groove which is situated between the tubercles of the humerus. At this point 

 an interruption in the fibrous stratum, beneath the transverse humeral ligament, 

 permits the long tendon of the biceps to escape from its interior. In addition to 

 the opening just referred to, there is another very constant deficiency in the 

 superior and anterior part of the fibrous stratum, where the narrowing tendon of 

 the subscapularis muscle is brought into contact with a bursa formed by a protrusion 

 of the synovial stratum. This defect in the fibrous stratum has its long axis in 

 the direction of the longitudinal fibres. Occasionally there is a similar but smaller 

 opening under cover of the tendon of the infraspinatus muscle. Through the two 

 Latter openings the joint cavity communicates with bursae situated between the 

 Capsule and the muscles referred to. 



The tendons of the subscapularis, supraspinatus, and infraspinatus muscles fuse 

 with, and so strengthen, the articular capsule as they approach their respective 

 insertions. 



On the superior aspect of the articulation the capsule is augmented by an 



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