Part 97

Relations.—Anteriorly, the stifle joint, the superficial flexor, popliteus, deep flexor, popliteal vessels, and tibial nerve; internally (above), the semitendinosus, semimembranosus, and adductor, (below) the fascia and skin; externally (above), the biceps femoris and peroneal (anterior tibial) nerve, (below) the fascia and skin.

FIG. 203.—MUSCLES OF LEG AND FOOT OF HORSE, INTERNAL VIEW.

r′, Tendon of semitendinosus; w, gracilis; x, sartorius; y, vastus internus. (After Ellenberger-Baum, Anat. für Künstler.) ]

Blood-supply.—Popliteal artery.

Nerve-supply.—Tibial nerve.

2. =Soleus= (Fig. 201).—This muscle is very small in the horse. It lies immediately under the deep fascia, on the proximal half of the outer surface of the leg, and is directed obliquely downward and backward.

Origin.—The head of the fibula.

Insertion.—The tendon of the gastrocnemius, about the middle of the leg.

Action.—To assist the gastrocnemius.

Structure.—It is a thin, fleshy band, about an inch (ca. 2 to 3 cm.) in width, terminating on a thin tendon which fuses with that of the gastrocnemius.

Relations.—Superficially, the skin, fascia, and peroneal nerve; deeply, the lateral extensor and deep flexor.

Blood-supply.—Posterior tibial artery.

Nerve-supply.—Tibial nerve.

3. =Superficial digital flexor= or =flexor pedis perforatus= (Figs. 199, 201, 203) (M. flexor digitalis pedis sublimis; superficial flexor of the phalanges).—The proximal part of this muscle lies between and under cover of the two heads of the gastrocnemius (Fig. 459). It consists almost entirely of a strong tendon, the belly being very little developed.

FIG. 204.—CROSS-SECTION OF LEFT LEG OF HORSE; SECTION IS CUT A LITTLE ABOVE MIDDLE OF REGION.

a, Tibia; b, fibula; c, tibialis anterior; d, peroneus tertius; e, anterior or long digital extensor; f, lateral extensor; g, deep head of deep flexor (flexor hallucis longus); h, inner head of deep flexor (flexor accessorius s, digitorum longus); i, superficial head of deep flexor (tibialis posterior); k, popliteus; l, superficial flexor tendon; m, gastrocnemius tendon; n, soleus; o, skin; p, anterior tibial artery; q, superficial peroneal nerve; q′, deep peroneal nerve; r, branch of q; s, posterior tibial artery; t, cutaneous nerve; u, tibial nerve; v, recurrent tibial vein; w, saphenous artery; x, saphenous vein; y, branches of saphenous nerve. (After Ellenberger, inl Leisering’s Atlas.) ]

Origin.—The supracondyloid fossa (Fossa plantaris) of the femur.

Insertion.—(1) The front and sides of the tuber calcis; (2) the eminences on the proximal extremity of the second phalanx, and the distal extremity of the first phalanx behind the lateral ligament.

Action.—To flex the digit and extend the hock joint. On account of the exceedingly small amount of muscular tissue the action is to be regarded chiefly as a mechanical effect, resulting from the action of other muscles on the stifle joint.

Structure.—The origin is by means of a strong round tendon which is incompletely covered with fleshy fibers as far as the upper third of the leg. It is pretty intimately attached to the gastrocnemius, especially to the outer head. At the distal third of the tibia it winds around the inner surface of the gastrocnemius tendon, and then occupies a position behind the latter. At the point of the hock it widens out, forming a sort of cap over the tuber calcis, detaching on either side a strong band which is inserted into the tuber calcis with the tarsal tendon of the biceps and semitendinosus. It then passes downward over the plantar (Calcaneo-metatarsal) ligament, becomes narrower, and is arranged below as in the thoracic limb. A large synovial bursa lies under the tendon from the distal fourth of the tibia to the middle of the tarsus. A =subcutaneous bursa= is sometimes found on the wide part of the tendon at the point of the hook. (Either or both of these bursæ may be involved in so-called “capped hock.”)

Relations.—Posteriorly, the gastrocnemius, fascia, and skin; anteriorly, the femoro-patellar capsule, the popliteus, the deep flexor, and the popliteal vessels; internally, the tibial nerve.

Blood-supply.—Femoro-popliteal artery.

Nerve-supply.—Tibial nerve.

FIG. 205.—INJECTED SYNOVIAL SHEATHS AND BURSÆ OF TARSAL REGION OF HORSE, INNER VIEW.

a, Synovial sheath of peroneus tertius and tibialis anterior; b, bursa under inner (cunean) tendon of tibialis anterior; c, synovial sheath of flexor longus s. accessorius; d, tarsal sheath of deep flexor; e, e′, bursa under superficial flexor tendon; f, f′, tibio-tarsal joint capsule; 1, anterior extensor; 2, tibialis anterior; 2′, inner (cunean) tendon of 2; 3, flexor longus; 4, deep digital flexor; 5, superficial flexor tendon; 6, gastrocnemius tendon; 7, tibia; 8, tarsus; 9, tuber calcis; 10, large metatarsal bone; 11, inner small metatarsal bone; 12, 12′, fascial bands. (After Ellenberger, in Leisering’s Atlas.) ]

FIG. 206.—INJECTED SYNOVIAL SHEATHS AND BURSÆ OF TARSAL REGION OF HORSE, EXTERNAL VIEW.

a, Synovial sheath of anterior or long digital extensor; b, synovial sheath of lateral digital extensor; c, c′, bursa under superficial flexor tendon; d, capsule of hock joint; 1, anterior or long extensor; 2, lateral extensor; 3, 3, 3, annular ligaments; 4, deep digital flexor; 5, tendon of gastrocnemius; 6, superficial flexor tendon; 7, tibia; 8, tarsus; 9, tuber calcis; 10, metatarsus. (After Ellenberger, in Leisering’s Atlas.) ]

4. =Deep digital flexor= or =flexor pedis perforans= (M. flexor digitalis pedis profundus; deep and oblique flexors of the phalanges).—The belly of this muscle lies on the posterior surface of the tibia, and is divisible into three parts or heads, which, however, finally unite on a common tendon of insertion.