JOINTS AND LIGAMENTS OF THE THORACIC LIMBS. The =shoulder-joint= is an arthrodial or ball-and-socket joint. The bones entering into its formation are the scapula and the humerus. The =capsular ligament= or =articular capsule= is very ample and allows for extended movement of the humerus. It is attached to the edge of the glenoid fossa of the scapula and passing distad covers the head of the humerus and is inserted at the line of junction of the shaft and the epiphysis which forms the head of the bone. On the lateral side of the ventral surface of the humerus the attachment continues distad about two centimeters along the lateral edge of the bicipital groove. On the medial side the insertion passes over the proximal end of the lesser tuberosity. A strong transverse band passes from the greater tuberosity to the lesser tuberosity and bridges the bicipital groove, converting it into a canal. The lateral and medial parts of the capsule are strengthened by thicker bands of fibres, the more prominent medial one of which passes from the coracoid process of the scapula to the lesser tuberosity. To the capsule are closely united parts of the supraspinatus, infraspinatus, coracobrachialis, and subscapularis muscles. A synovial membrane lines the capsule within and forms a sheath around the biceps tendon, so that the latter does not actually enter the synovial capsule. The =elbow-joint= (Figs. 52 and 53) is a ginglymus or hinge-joint. The bones which enter into it are the humerus, radius, and ulna. The capsule of the joint forms a sac, with the following attachments to the bones: (1) To the humerus it is attached at the proximal edge of the coronoid and radial fossæ; to the sides of the capitulum and trochlea distad of the two epicondyles, and to the distal edge of the olecranon fossa. (2) To the ulna it is attached at the edges of the radial and semilunar notches; (3) to the radius around the articular facet, two or three centimeters distad of the border. Many of the muscles of this region are closely attached to the capsule. [Illustration: FIG. 52.--LIGAMENTS OF ELBOW-JOINT, MEDIAL SIDE. FIG. 53.--ELBOW-JOINT, LATERAL VIEW. Fig. 52.--1, humerus; 2, ulna; 3, radius. _a_ and _b_, the two medial collateral ligaments. Fig. 53.--1, humerus; 2, radius; 3, ulna. _a_, dorsal collateral ligament; _b_, ventral collateral ligament; _c_, annular ligament.] Closely connected with the capsule of the joint are the =collateral ligaments=. The two =medial= collateral ligaments (Fig. 52) arise from the medial epicondyle. One (_b_) passes distad and laterad to the interval between the radius and ulna; here it divides, one branch going to the head of the radius, while the other is attached to the lateral surface of the ulna at the edge of the semilunar notch. The second medial ligament (_a_) lies dorsad of the first; it passes to the medial surface of the ulna, at the distal edge of the semilunar notch.