126 THE SUPERIOR EXTREMITY 



and is attached to its rim. It deepens, and at the same 

 time serves to extend, the articular socket of the scapula. 

 The intimate connection which it presents with the capsule 

 of the joint can now be studied. Two tendons are also 

 closely associated with it, viz. the long head of the triceps 

 brachii below, and the long head of the biceps brachii above. 



Long Head of the Biceps. The tendon of the long 

 head of the biceps is an important factor in the mechanism 

 of the shoulder- joint. It enters the capsule through the 

 opening between the two tubercles of the humerus, and 

 is prolonged over the head of the bone to the apex of the 

 glenoid cavity. Its attachment to the scapula should now be 

 examined. The tendon divides into three portions, viz. a 

 large intermediate part, which obtains direct attachment to 

 the scapula, and two smaller collateral parts, which diverge 

 from each other and blend with the labrum glenoidale. The 

 long head of the biceps brachii, by its position within the 

 capsule and in the deep sulcus between the tubercles of the 

 humerus, serves to keep the head of the bone in place, and 

 to steady it in the various movements at the shoulder-joint. 



The synovial stratum lines the fibrous stratum of the 

 capsule of the joint, and is reflected from it upon the anatomical 

 neck of the humerus as far as the articular margin of the 

 head of the bone. The bursal protrusion of the bursa sub- 

 scapularis, under the tendon of the subscapularis muscle, has 

 already been noticed. The tendon of the biceps, as it 

 traverses the joint, is enveloped in a tubular sheath of the 

 membrane \ this sheath bulges out through the opening of the 

 capsule in the form of a bursa which lines the intertuber- 

 cular sulcus (Fig. 53). 



Articular Surfaces. The smooth, glistening articular 

 cartilage which coats the head of the humerus is thickest 

 in the centre, and thins as it passes towards the edges. In 

 the case of the glenoid cavity the reverse of this will be 

 noticed. 



Movements at the Shoulder-joint. The shoulder is a 

 ball-and-socket joint (enarthrosis), and consequently move- 

 ment in every direction is permitted, viz. (i) flexion, or 

 forward movement; (2) extension, or backward movement 

 (checked in its extent by the coraco-humeral ligament) ; (3) 

 abduction, or lateral movement (checked by the coraco- 

 acromial arch) ; (4) adduction, or medial movement (limited 



