=Movements.=—While it is a typical enarthrosis in structure, and capable of the various movements of the ball-and-socket joint, the chief normal movements are flexion and extension. In the position of rest the angle formed between the scapula and humerus posteriorly is about 110° to 120°; in flexion it is reduced to about 80°, and in extension it is increased to about 145°. Adduction and abduction are very restricted, the former being limited chiefly by the infraspinatus, the latter by the subscapularis and the low insertion of the superficial pectoral muscles. Rotation is somewhat freer, but does not exceed 33°, when all the muscles are removed (Franck). THE ELBOW JOINT This, the cubital articulation (Articulatio cubiti), is a ginglymus formed between the distal extremity of the humerus and the proximal ends of the bones of the forearm. [Illustration: FIG. 143.—LEFT ELBOW JOINT OF HORSE, POSTERIOR VIEW. THE CAPSULE IS REMOVED. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ] The =articular surfaces= are: (1) A trochlear surface formed by the condyles of the humerus and the groove between them; (2) the corresponding glenoid cavities and ridge on the proximal extremity of the radius, together with the semilunar notch of the ulna. The articular surface of the condyles does not extend upon the back of the extremity, but the groove which receives the semilunar notch of the ulna extends up into the olecranon fossa. In the fore part of the groove there is a synovial fossa. The surface on the outer condyle is smaller than that of the inner one, and is subdivided into two unequal parts by a shallow furrow. On the lower part of the semilunar notch and the adjacent part of the ridge on the radius are synovial fossæ. The =joint capsule= is extremely thin behind, where it forms a pouch in the olecranon fossa under the anconeus muscle and a pad of fat. In front it is strengthened by oblique fibers (Ligamentum obliquum or anterior ligament), and laterally it fuses with the lateral ligaments. Small pouches of the =synovial membrane= lubricate the origins of the flexors of the carpus and digit and the small radio-ulnar joints. There are two lateral ligaments. The =internal lateral ligament= (Ligamentum collaterale radiale) is attached above to an eminence on the internal epicondyle of the humerus, and divides into two parts: the long, superficial part ends on the inner border of the radius, just below the level of the interosseous space; the deep, short part is inserted into the internal tuberosity of the radius. (The superficial part represents the pronator teres muscle, which is only exceptionally present in the horse.) The =external lateral ligament= (Ligamentum collaterale ulnare) is short and strong. It is attached above to a depression on the external epicondyle of the humerus, and below to the external tuberosity of the radius, just below the margin of the articular surface.