Part 86

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.

FIG. 193.—DEEPER MUSCLES OF FOREARM OF HORSE, INTERNAL VIEW.

23, Internal head of triceps; 30, flexor carpi medius; 31, flexor carpi internus; 31′, tendon of 31; 32, superficial digital flexor; 32′, radial check ligament; 32″, tendon of superficial flexor; 33a, 33b, 33c, humeral heads of deep flexor; 33′, deep flexor tendon; 33″, subcarpal check ligament; 34, ulnar head of deep flexor; 35, radial head of deep flexor; 36, suspensory ligament. (After Ellenberger, in Leisering’s Atlas.) ]

3. =Flexor carpi externus= (M. extensor carpi ulnaris s. ulnaris lateralis; external flexor of the metacarpus).—This muscle lies on the outer face of the forearm, behind the lateral extensor of the digit.

Origin.—The extensor (external) epicondyle of the humerus, behind and below the lateral ligament.

Insertion.—(1) The outer surface and upper edge of the accessory carpal bone; (2) the proximal extremity of the outer (fourth) metacarpal bone.

Action.—To flex the carpal joint and to extend the elbow.

Structure.—The belly of the muscle is flattened and is intersected by a good deal of tendinous tissue. There are two tendons of insertion. The short tendon is inserted into the accessory carpal bone. The long tendon is detached just above the carpus; it is smaller and rounded; it passes downward and a little forward through a groove on the outer surface of the accessory carpal bone, enveloped by a =synovial sheath=, to reach its insertion on the outer metacarpal bone. A synovial pouch lies under the origin of the muscle at the elbow joint, with the cavity of which it communicates.

FIG. 194.—CROSS-SECTION OF PROXIMAL PART OF LEFT CARPUS OF HORSE.

The tendons have been removed to show the canals in which they lie. The joint cavity is black. By an oversight the carpal canal for the two flexor tendons behind the posterior ligament of the carpus is not marked. Cr, Radial, Ci, intermediate, Cu, ulnar, Ca, accessory carpal bones. ]

Relations.—Superficially, the skin, fascia, and cutaneous branches of the ulnar nerve; deeply, the elbow joint, the ulna, and the flexors of the digit; in front, the lateral extensor of the digit; behind, the middle flexor of the carpus, the ulnar head of the deep flexor, and the ulnar vessels and nerve.

Blood-supply.—Interosseous, ulnar, and median arteries.

Nerve-supply.—Radial nerve.

4. =Superficial digital flexor= or =flexor perforatus= (M. flexor digitalis sublimis; superficial flexor of the phalanges).—This muscle is situated in the middle of the flexor group, chiefly under cover of the middle flexor of the carpus.

Origin.—(1) The flexor epicondyle of the humerus, between the flexor carpi internus and the deep flexor of the digit; (2) a ridge on the posterior surface of the radius, below its middle and near the internal border.

Insertion.—(1) The eminences on the proximal extremity of the second phalanx behind the lateral ligaments; (2) the distal extremity of the first phalanx, also behind the lateral ligaments.

Action.—To flex the digit and carpus, and to extend the elbow.

FIG. 195.—SYNOVIAL SHEATHS AND BURSÆ OF LOWER PART OF RIGHT FORE LIMB OF HORSE, INTERNAL VIEW.

a, Sheath of extensor carpi obliquus; b, sheath of flexor carpi internus; c, carpal sheath; d, d′ d″, d‴, digital sheath; e, bursa under anterior extensor tendon; f, capsule of fetlock joint; 1, extensor carpi radialis; 2, tendon of extensor carpi obliquus; 3, flexor carpi internus; 4, flexor carpi medius; 5, superficial flexor tendon; 6, deep flexor tendon; 7, suspensory ligament; 8, small metacarpal bone; 9, large metacarpal bone; 10, posterior annular ligament of fetlock; 11, proximal digital annular ligament; 12, radius; 13, radio-carpal joint; 14, fetlock joint; 15, lateral cartilage; 16, band from first phalanx to lateral cartilage. (After Ellenberger, in Leisering’s Atlas.)

The synovial sheaths (colored yellow) and the joint capsules (colored pink) are injected. ]

FIG. 196.—SYNOVIAL SHEATHS AND BURSÆ OF LOWER PART OF RIGHT FORE LIMB OF HORSE, EXTERNAL VIEW.

a, Sheath of extensor carpi radialis; b, sheath of anterior extensor; c, sheath of lateral extensor; d, sheath of outer tendon of flexor carpi externus; e, e′, carpal sheath; f, f′ f″, digital sheath; g, bursa under anterior extensor tendon; h, bursa under lateral extensor tendon; i, capsule of fetlock joint; 1, extensor carpi radialis; 2, anterior digital extensor; 3, lateral digital extensor; 4, flexor carpi externus; 4′ 4″, tendons of 4; 5, superficial flexor tendon; 6, deep flexor tendon; 7, suspensory ligament; 8, external metacarpal bone; 9, large metacarpal bone; 10, posterior annular ligament of fetlock; 11, digital annular ligament; 12, fetlock joint; 13, lateral cartilage; 14, band from first phalanx to lateral cartilage. (After Ellenberger, in Leisering’s Atlas.) ]