_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.[73]
_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.
[Illustration:
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.
[Illustration:
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.)
]
[Illustration:
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.
_Origin._—(1) The posterior edge of the external condyle of the tibia;
(2) the external border of the external condyle of the tibia, just
behind the facet for the fibula; (3) the middle third of the posterior
surface and the upper part of the external border of the tibia, the
posterior border of the fibula, and the interosseous ligament.[74]
_Insertion._—The semilunar crest of the third phalanx and the adjacent
surface of the lateral cartilage.
_Action._—To flex the digit and to extend the hock joint.
_Structure._—(1) The inner head (M. flexor digitalis longus s. flexor
accessorius) is easily isolated (Figs. 203, 459). It has a fusiform
belly, which crosses the leg obliquely and lies in a groove formed by
the other heads and the popliteus. This terminates near the lower third
of the tibia on a round tendon which passes downward, partly embedded in
the internal lateral ligament of the hock, and joins the common tendon
about a third of the way down the metatarsus. In its course over the
inner surface of the hock the tendon lies in a canal formed by the
strong tarsal fascia, the tibia, and the lateral ligament, and is
provided with a =synovial sheath= which extends from the distal fourth
of the tibia to the junction with the principal tendon. (2) The
superficial head (M. tibialis posterior) is only partially separable. It
has a flattened belly, terminating near the lower third of the tibia on
a flat tendon which soon fuses with the principal tendon. (3) The deep
head (M. flexor hallucis longus) is much the largest. It lies on the
posterior surface of the tibia, from the popliteal line outward and
downward. The belly contains much tendinous tissue, and terminates
behind the distal end of the tibia on a strong round tendon. The latter
receives the tendon of the tibialis posterior, passes downward in the
tarsal groove, bound down by the strong tarsal fascia (Ligamentum
laciniatum) and enveloped in a synovial sheath, receives the tendon of
the inner head below the hock, and, a little further down, the so-called
check ligament (Caput tendineum [Schmaltz]). The =tarsal sheath= (Vagina
tarsea) begins about two to three inches (ca. 5 to 7.5 cm.) above the
level of the internal malleolus, and extends about one-fourth of the way
down the metatarsus. (Distention of the sheath, as in “thoroughpin,”
affects chiefly its proximal end.) The check ligament resembles that of
the fore limb, except that it is longer and very much weaker; it may be
absent. The remainder of the tendon is arranged like that of the
thoracic limb.
_Relations._—Anteriorly, the tibia and fibula, the popliteus, lateral
extensor, tibialis anterior, and the tibial vessels; posteriorly, the
gastrocnemius, superficial flexor, and the tibial nerve; externally, the
fascia, skin, and the soleus; internally, the fascia and skin.
_Blood-supply._—Posterior tibial artery.
_Nerve-supply._—Tibial nerve.
5. =Popliteus= (Fig. 203).—This thick and triangular muscle lies on the
posterior surface of the femoro-tibial articulation and the posterior
surface of the tibia above the popliteal line.
_Origin._—A small depression on the external epicondyle of the femur,
close to the articular surface and under the lateral ligament.
_Insertion._—A triangular area on the posterior surface of the tibia,
above and internal to the popliteal line; also the proximal half of the
inner border and a narrow adjacent part of the internal surface of the
tibia.
_Action._—To flex the femoro-tibial joint and to rotate the leg inward.
_Structure._—The strong tendon of origin lies at first under the lateral
ligament, and curves backward and inward over the external condyle of
the tibia and its semilunar cartilage, being invested by a reflection of
the synovial capsule of the joint (Fig. 459). The tendon is succeeded by
a thick triangular belly, the fibers of which are directed obliquely
downward and inward.
_Relations._—Superficially, the fascia and skin, semitendinosus,
gastrocnemius, superficial flexor; deeply, the femoro-tibial joint, the
tibia, the popliteal vessels and their divisions. The saphenous vessels
and nerve lie along the inner border of the muscle, separated from it,
however, by the deep fascia.
_Blood-supply._—Popliteal and posterior tibial arteries.
_Nerve-supply._—Tibial nerve.