Henry Gray (18251861). Anatomy of the Human Body. 1918.
these, the capsule is strengthened in front by two bands derived from the tendons of the Pectoralis major and Teres major respectively.
The Transverse Humeral Ligament(Fig. 327) is a broad band passing from the lesser to the greater tubercle of the humerus, and always limited to that portion of the bone which lies above the epiphysial line. It converts the intertubercular groove into a canal, and is the homologue of the strong process of bone which connects the summits of the two tubercles in the musk ox.
The Glenoidal Labrum (labrium glenoidale; glenoid ligament) is a fibrocartilaginous rim attached around the margin of the glenoid cavity. It is triangular on section, the base being fixed to the circumference of the cavity, while the free edge is thin and sharp. It is continuous above with the tendon of the long head of the Biceps brachii, which gives off two fasciculi to blend with the fibrous tissue of the labrum. It deepens the articular cavity, and protects the edges of the bone.
Synovial Membrane.The synovial membrane is reflected from the margin of the glenoid cavity over the labrum; it is then reflected over the inner surface of the capsule, and covers the lower part and sides of the anatomical neck of the humerus as far as the articular cartilage on the head of the bone. The tendon of the long head of the Biceps brachii passes through the capsule and is enclosed in a tubular sheath of synovial membrane, which is reflected upon it from the summit of the glenoid cavity and is continued around the tendon into the intertubercular groove as far as the surgical neck of the humerus (Fig. 327). The tendon thus traverses the articulation, but it is not contained within the synovial cavity.
Bursæ.The bursæ in the neighborhood of the shoulder-joint are the following: (1) A constant bursa is situated between the tendon of the Subscapularis muscle and the capsule; it communicates with the synovial cavity through an opening in the front of the capsule; (2) a bursa which occasionally communicates with the joint is sometimes found between the tendon of the Infraspinatus and the capsule; (3) a large bursa exists between the under surface of the Deltoideus and the capsule, but does not communicate with the joint; this bursa is prolonged under the acromion and coraco-acromial ligament, and intervenes between these structures and the capsule; (4) a large bursa is situated on the summit of the acromion; (5) a bursa is frequently found between the coracoid process and the capsule; (6) a bursa exists beneath the Coracobrachialis; (7) one lies between the Teres major and the long head of the Triceps brachii; (8) one is placed in front of, and another behind, the tendon of the Latissimus dorsi.
The muscles in relation with the joint are, above, the Supraspinatus; below, the long head of the Triceps brachii; in front, the Subscapularis; behind, the Infraspinatus and Teres minor; within, the tendon of the long head of the Biceps brachii. The Deltoideus covers the articulation in front, behind, and laterally.
The arteries supplying the joint are articular branches of the anterior and posterior humeral circumflex, and transverse scapular.
The nerves are derived from the axillary and suprascapular.
Movements.The shoulder-joint is capable of every variety of movement, flexion, extension, abduction, adduction, circumduction, and rotation. The humerus is flexed (drawn forward) by the Pectoralis major, anterior fibers of the Deltoideus, Coracobrachialis, and when the forearm is flexed, by the Biceps brachii; extended (drawn backward) by the Latissimus dorsi, Teres major, posterior fibers of the Deltoideus, and, when the forearm is extended, by the Triceps brachii; it is abducted by the Deltoideus and Supraspinatus; it is adducted by the Subscapularis, Pectoralis major, Latissimus dorsi, and Teres major, and by the weight of the limb; it is rotated outward by the Infraspinatus and Teres minor; and it is rotated inward by the Subscapularis, Latissimus dorsi, Teres major, Pectoralis major, and the anterior fibers of the Deltoideus.
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 this latter is supplemented by the glenoidal labrum. (2) The looseness of the capsule of the joint. (3) The intimate connection of the capsule with the muscles attached to the head of the humerus. (4) The peculiar relation of the tendon of the long head of the Biceps brachii to the joint.