_Relations._—Superficially, the skin and fascia, the posterior superficial pectoral and the tensor fasciæ antibrachii; deeply, the elbow joint, the radius, the deep flexor, the flexor carpi medius, the posterior radial vessels, and the median nerve. At the elbow the artery and nerve lie in front of the muscle, but below they dip beneath it. _Blood-supply._—Posterior radial artery. _Nerve-supply._—Median nerve. On removing the deep fascia on the inner surface of the elbow the student may notice a small muscle lying along the lateral ligament. This is the =pronator teres=, which is usually not present or a mere vestige in the horse. It arises by a small, flat tendon from the flexor epicondyle of the humerus, and is inserted into the internal lateral ligament of the elbow. On account of its small size and the fact that the forearm is fixed in the position of pronation, the muscle can have no appreciable function. It is usually represented by the long portion of the internal lateral ligament. 2. =Flexor carpi medius= (M. flexor carpi ulnaris s. ulnaris medialis; oblique or middle flexor of the metacarpus).—This muscle lies on the inner and posterior aspect of the forearm partly under, partly behind, the preceding muscle. It arises by two heads—humeral and ulnar. _Origin._—(1) The flexor (internal) epicondyle of the humerus just behind the preceding muscle; (2) the inner surface and posterior border of the olecranon. _Insertion._—The upper edge of the accessory carpal (pisiform) bone. _Action._—To flex the carpal joint, and to extend the elbow. _Structure._—The humeral head is much the larger, constituting, in fact, the bulk of the muscle. It is flattened, curved, and tapers at both ends. The ulnar head, much smaller and very thin, is covered by an aponeurosis from which many of its fibers arise. It joins the large head a little above the middle of the forearm. The tendon of insertion is short and strong; it blends with the posterior annular ligament of the carpus. _Relations._—Superficially, the tensor fasciæ antibrachii, superficial pectoral, and flexor carpi internus, the skin and fascia, and cutaneous branches of the ulnar nerve; deeply, the superficial and deep flexors of the digit. In the distal half of the forearm the ulnar vessels and nerve lie between the outer edge of this muscle and the external flexor of the carpus. _Blood-supply._—Ulnar and posterior radial arteries. _Nerve-supply._—Ulnar and median nerves. [Illustration: FIG. 193.—DEEPER MUSCLES OF FOREARM OF HORSE, INTERNAL VIEW.