SHOULDER-JOINT 303 



of the upper part of the bicipital groove. It is a thin, ribbon-like band, occasion- 

 ally quite free from the capsule. 



The transverse humeral ligament is a prolongation of the capsular ligament. 

 It is a broad band of fibrous tissue passing from the lesser to the greater tuber- 

 osity of the humerus, and always limited to that portion of the bone which lies 

 above the epiphyseal line. It converts the bicipital groove into an osseoaponeu- 

 rotic canal, and is the homologue of the strong process of bone which connects 

 the summits of the two tuberosities in the musk ox. 



The glenoid ligament (labrum glenoidale) (Figs. 245 and 247) is a fibrocartilagi- 

 nous rim, attached around the margin of the glenoid cavity. It is triangular on 

 section, the thickest portion being fixed to the circumference of the cavity, the 

 free edge being thin and sharp. It is continuous above with the long tendon 

 of the Biceps muscle, which bifurcates at the upper part of the cavity into two 

 fasciculi, and becomes continuous with the fibrous tissue of the glenoid ligament. 

 This ligament deepens the cavity for articulation, and protects the edges of the 

 bone. 



Synovial Membrane (Fig. 247). The synovial membrane is reflected from the margin of 

 the glenoid cavity over the fibrocartilaginous rim surrounding it; it is then reflected over the 

 internal surface of the capsular ligament, covers the lower part and sides of the anatomical neck 

 of the humerus as far as the cartilage covering the head of the bone. The long tendon of the 

 Biceps brachii, which passes through the capsular ligament, is enclosed in a tubular sheath of 

 synovial membrane (vagina mucosa intertubercularis) , which is reflected upon it at the point 

 where it perforates the capsule, and is continued around it as far as the level of the surgical 

 neck of the humerus. The tendon of the Biceps is thus enabled to traverse the articulation, but 

 it is not contained in the interior of the synovial cavity. 



Bursae. A large bursa, the subscapuiar bursa, exists between the joint capsule and the ten- 

 don of the Subscapularis muscle. This sac communicates with the shoulder-joint by means 

 of an opening at the inner side of the capsular ligament. Occasionally another and smaller bursa, 

 the infraspinatus bursa, exists beneath the tendon of the Infraspinatus. It communicates with 

 the shoulder-joint by means of an opening in the outer surface of the capsule. The subdeltoid 

 or subacromial bursa is placed between the under surface of the Deltoid muscle and the outer 

 surface of the capsule. It does not communicate with the joint. The subcutaneous acromial 

 bursa is between the surface and the summit of the acromion process. There is a bursa beneath 

 the Coracobrachialis muscle, one beneath the Teres major, and one beneath the tendinous 

 portion of the Latissimus dorsi. There is also a bursa between the tendon of insertion of 

 the Pectoralis major muscle and the long head of the Biceps. 



The muscles in relation with the joint are, above, the Supraspinatus; below, the long head of 

 the Triceps; in front, the Subscapularis ; behind, the Infraspinatus and Teres minor; within, the 

 long tendon of the Biceps. The Deltoid is placed most externally, and covers the articulation 

 on its outer side, as well as in front and behind. 



The arteries supplying the joint are articular branches of the anterior and posterior circum- 

 flex, and the suprascapular. 



The nerves are derived from the circumflex and suprascapular. 



Movements. The shoulder-joint is capable of movement in every direction, forward, back- 

 ward, abduction, adduction, circumduction, and rotation. The humerus is drawn forward by 

 the Pectoralis major, anterior fibres of the Deltoid, Coracobrachialis, and by the Biceps when 

 the forearm is flexed; backward, by the Latissimus dorsi, Teres major, posterior fibres of the Del- 

 toid, and by the Triceps when the forearm is extended; it is abducted (elevated) by the Del- 

 toid and Supraspinatus; it is adducted (depressed) by the Subscapularis, Pectoralis major, Latis- 

 simus dorsi, and Teres major; it is rotated outivard by the Infraspinatus and Teres minor; and 

 it is rotated inward by the Subscapularis, Latissimus dorsi, Teres major, and Pectoralis major. 



The most striking peculiarities in this joint are: (1) The large size of the head of the humerus 

 in comparison with the depth of the glenoid cavity, even when supplemented by the glenoid 

 ligament. (2) The looseness of the capsule of the joint. (3) The intimate connection of the cap- 

 sule with the muscles attached to the head of the humerus. (4) The peculiar relation of the 

 Biceps tendon to the joint. 



It is in consequence of the relative size of the two articular surfaces that the joint enjoys such 

 free movement in every possible direction. When these movements of the arm are arrested in 

 the shoulder-joint by the contact of the bony surfaces and by the tension of the corresponding 

 fibres of the capsule, together with that of the muscles acting as accessory ligaments, they can 

 be carried considerably farther by the movements of the scapula, involving, of course, motion at 



