THE MUSCLES OP THE LEG AND FOOT 335 



fleshy part near the tarsus. It passes do'\vnward over the front of the hock, bound 

 down by the three annular hgaments 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. 



Eek^ions.— 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). i— This muscle lies 

 on the lateral surface of the leg, behind the preceding one. 



Ongwi.— 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 cm.) above the lateral malleolus and ends about one and one- 

 half inches (ca. 3 to 4 cm.) 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).^ — 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 underljdng 

 prolongation of the synovial membrane of the femoro-tibial joint have been men- 

 tioned in the description of the long extensor. The superflcial face gives origin 

 to fibers of the long extensor in the upper part of the leg, and the deep face is fusecL--T 

 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 

 and 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. 



^ 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. 



