1, Semi-tendinosus; 2, semi-membranosus; 3, triceps cruris (vastus internus); 4, patella; 5, sartorius; 6, gracilis; 7, extensor longus digitorum common extensor of the toes (anterior extensor of the phalanges); 8, tendon of the preceding muscle; 9, reinforcing band given off by the suspensory ligament of the fetlock; 10, tibialis anticus (flexor of the metatarsus), its tendinous portion; 11, tibialis anticus (flexor of the metatarsus), its fleshy portion; 12, cuneiform branch of the tendon of this fleshy portion; 13, internal head of gastrocnemius; 14, popliteus; 15, tendon of the flexor brevis digitorum (superficial flexor of the phalanges); 16, flexor longus pollicis and tibialis posticus (deep flexor of the phalanges); 17, flexor longus digitorum (oblique flexor of the phalanges); 18, 18, tendon of the superficial flexor of the phalanges; 19, 19, tendon of the deep flexor of the phalanges; 20, suspensory ligament of the fetlock; 21, principal metatarsal; 22, internal rudimentary metatarsal.
In the pig the general arrangement of the muscle is similar, but the tendons end in a manner which is a little more complicated. Apart from the fasciculi which correspond to the tendinous portion of the tibialis anticus (fleshy here, as in the ox), the long extensor of the toes at the level of the tarsus divides into three tendons: the internal goes to the great internal toe; the middle bifurcates in the upper part of the digital portion of the foot, and each of its branches goes towards one of the great-toes; the external divides to pass towards each of the two small toes, and towards the great ones; but this latter disposition is not constant.
By its contraction the muscle which we have just studied extends the phalanges and flexes the foot.
Peroneus Tertius.—This muscle is not found in domestic quadrupeds.
We should remember, nevertheless, that certain authors consider as representing it the tendinous portion of the anterior tibial of the horse, or the corresponding portion now fleshy, of the same muscle in the pig and the ox. It is by reason of this fact that it is called the third peroneal, notwithstanding that in the numerical order of the peroneals it is rather the first.
But that which still further complicates this question of nomenclature is that some authors give this name of third to a peroneal which, in the carnivora, is situated more definitely in the group of external muscles (see [below], Short Lateral Peroneal).
Muscles of the External Region
In man, two muscles constitute this region; they are the peroneus longus and peroneus brevis.
Peroneus Longus ([Fig. 84], 9; [Fig. 85], 7).—This muscle does not exist in the domestic animals; only in the flesh-eaters, the pig and the ox excepted.
It is in relation superiorly with the tibialis anticus, and inferiorly with the common extensor of the toes; in the ox, it is in contact with this latter muscle throughout its whole length.