THE MUSCLES OF THE LEG AND FOOT 335 
fleshy part near the tarsus. It passes downward over the front of the hock, bound 
down by the three annular ligaments already described (see tarsal fascia), and en- 
veloped by a synovial sheath which begins a little above the level of the lateral 
malleolus, and extends nearly to the junction with the lateral extensor tendon. 
This union occurs usually about a hand’s breadth below the tarsus. In the angle 
-of union the extensor brevis also joins the principal tendon. Beyond this point 
the arrangement is the same as in the fore limb. 
Relations.—Superficially, the skin and fascia; deeply, the femoro-tibial joint, 
peroneus tertius, and tibialis anterior; behind, the lateral extensor and the super- 
’ ficial and deep peroneal nerves. In front of the tarsus the anterior tibial artery 
crosses the deep face of the tendon (Fig. 585). 
Blood-supply.— Anterior tibial artery. 
Nerve-supply.—Peroneal nerve. 
2. Lateral digital extensor (M. extensor digitalis lateralis)..—This muscle lies 
on the lateral surface of the leg, behind the preceding one. 
Origin.—The lateral ligament of the stifle joint, the fibula, the lateral border 
of the tibia, and the interosseous ligament. 
Insertion —The tendon of the long extensor, about a third of the way down 
the metatarsus. 
Action —To assist the long extensor. 
Structure—The belly is fusiform, flattened, and pennate. The tendon runs 
through the entire length of the belly and becomes free from it at the distal fourth 
of the tibia. It descends through the groove on the lateral malleolus, bound down 
by an annular ligament, and, inclining forward, blends (usually) with the tendon 
of the long extensor. It is provided with a synovial sheath, which begins about 
an inch (ca. 2 to 3 em.) above the lateral malleolus and ends about one and one- 
half inches (ca. 3 to 4 em.) above the junction. Sometimes the fusion does not 
occur; the tendon then descends alongside of that of the long extensor, and is in- 
serted into the first phalanx like the corresponding muscle of the thoracic limb. 
Relations—Laterally, the skin and fascia and the superficial peroneal nerve; 
medially, the tibia and fibula; anteriorly, the intermuscular septum, the long 
extensor, and the tibialis anterior; posteriorly, the deep digital flexor and the soleus. 
Blood-supply.—Anterior tibial artery. 
Nerve-supply.—Peroneal nerve. 
3. Peroneus tertius (Tendo femoro-metatarseus).2—This consists in the horse 
of a strong tendon which lies between the long extensor and the tibialis anterior. 
Origin.—The extensor fossa (between the lateral condyle and the trochlea 
of the femur), in common with the long extensor. 
Insertion —(1) The proximal extremity of the large (third) metatarsal bone 
and the third tarsal bone; (2) the fibular and fourth tarsal bones. 
Action—Mechanically to flex the hock when the stifle joint is flexed. 
Structure—It is entirely tendinous. The proximal end and the underlying 
prolongation of the synovial membrane of the femoro-tibial joint have been men- 
tioned in the description of the long extensor. The superficial face gives origin 
to fibers of the long extensor in the upper part of the leg, and the deep face is fused 
with the tibialis anterior except at either end of the region. At the distal end of the 
tibia the tendon is perforated for the emergence of the tendon of the tibialis anterior 
and divides into two branches. The anterior branch is attached to the third tarsal 
ard third metatarsal bones, while the lateral one curves outward, bifurcates, and 
1 Also known as the peroneus or the lateral extensor of the phalanges. Lesbre considers it 
to be the homologue of the peroneus brevis of man and other pentadactyls. 
__, 7*It seems inadvisable to retain the old term, tendinous part of the flexor metatarsi, since it 
is inapplicable to other domesticated animals in which the muscle is well developed (e. g., pig). 
Schmaltz uses the term tendo femoro-tarseus, and Varaldi and Lesbre designate it the femoro- 
metatarsal cord. The name peroneus anterior has also been proposed. 
