252 THE ARTICULATIONS. 



be seen only when the capsule is opened. It is attached above to the apex of the 

 glenoid cavity, close to the root of the coracoid process, and, passing downward 

 along the inner edge of the tendon of the Biceps, is attached below to the lesser 

 tuberosity of the humerus, where it forms the inner boundary of the upper part of 

 the bicipital groove. It is a thin, ribbon-like band, occasionally quite free from 

 the capsule. 



The Transverse Humeral Ligament. This is a broad band of fibrous tissue 

 passing from the lesser to the greater tuberosity of the humerus, and always 

 limited to that portion of the bone which lies above the epiphyseal line. It con- 

 verts the bicipital groove into an osseo-aponeurotic canal, and is the analogue of 

 the strong process of bone which connects the summits of the two tuberosities in 

 the musk ox. 



The G-lenoid Ligament is a fibro-cartilaginous rim, attached round 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. It is lined by the synovial 

 membrane. 



The Synovial Membrane is reflected from the margin of the gienoid cavity over 

 the fibro-cartilaginous 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 muscle which passes through the capsular ligament is 

 enclosed in a tubular sheath of synovial membrane, which is reflected upon it at 

 the point where it perforates the capsule, and is continued around it as far as the 

 summit of the glenoid cavity. The tendon of the Biceps is thus enabled to 

 traverse the articulation, but it is not contained in the interior of the synovial 

 cavity. The synovial membrane communicates with a large bursal sac beneath 

 the tendon of the Subscapularis by an opening at -the inner side of the capsular 

 ligament ; it also occasionally communicates with another bursal sac, beneath the 

 tendon of the Infraspinatus, through an orifice at its posterior part. A third 

 bursal sac, which does not communicate with the joint, is placed between the under 

 surface of the Deltoid and the outer surface of the capsule. 



The Muscles in relation with the joint are, above, the Supraspinatus; below, 

 the long head of the Triceps ; in front, the Subscapularis ; behind, the Infra- 

 spinatus 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 circumflex, and suprascapular. 



The Nerves are derived from the circumflex and suprascapular. 



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

 backward, abduction, adduction, circumduction, and rotation. The humerus is 

 drawn forward by the Pectoralis major, anterior fibres of the Deltoid, Coraco- 

 brachialis, and by the Biceps when the forearm is flexed ; backward, by the Latis- 

 simus dorsi, Teres major, posterior fibres of the Deltoid, and by the Triceps when 

 the forearm is extended ; it is abducted (elevated) by the Deltoid and Supraspinatus ; 

 it is adducted (depressed) by the Subscapularis, Pectoralis major, Latissimus dorsi, 

 and Teres major ; it is rotated outward 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 



