Terminal branches of the posterior tibial artery.
— When the tibial artery reaches the hollow of the calcaneum, and gets beneath the origin of the abductor pollicis, it divides into the two plantar arteries, which, from their position, are named internal and external. The internal plantar artery, [a. plantaris interna] much smaller than the other, is directed forwards, along the inner side of the foot. Placed at first (in the position of the foot during the erect posture) above the abductor pollicis, and afterwards between it and the short flexor of the toes, it gives branches to both ; and also some offsets which incline towards the inner border of the foot, and communicate with branches of the dorsal arteries. On reaching the extremity of the first metatarsal bone, the internal plantar artery, considerably diminished in size, terminates by running along the inner border of the great toe, anastomosing with its digital branches. The direction of the artery corresponds with that of the line which separates the internal from the middle set of plantar muscles.
The external plantar artery, [a. plantaris externa] much larger than the internal plantar, at first inclines outwards and then forwards, to reach the base of the fifth metatarsal bone : thence, changing its direction, it turns obliquely inwards across the foot, to gain the interval between the bases of the first and second metatarsal bones, where it joins, by a communicating branch, with the dorsal artery of the foot; and thus is completed the plantar arch, the convexity of which is turned forward. In this long course the vessel lies at different degrees of depth. At first it is placed, together with the external plantar nerve, between the calcaneum and the abductor pollicis; then between the flexor brevis digitorum and flexor accessorius. As it turns forwards it lies comparatively near the surface in the interval between the short flexor of the toes and the abductor of the little toe, being placed along the line separating the middle from the external portion of the plantar fascia ; by which membrane, and by the integuments and fat, the vessel is here covered. The remainder of the artery, which turns inwards and forms the plantar arch, is situated deeply against the interosseous muscles, and is covered by the flexors of" the toes and the lumbricales muscles.
From the plantar arch numerous branches are given off, varying in size and importance. Of these some pass outwards over the border of the foot, and anastomose with the dorsal arteries ; others go back to supply the parts in the hollow of the foot; and several down to the fascia, integument, and subcutaneous cellular substance. These branches are too irregular to admit of being named or described.
From its upper and fore part branches are given off which require particular notice.
The posterior perforating branches, (perforantes post.) three in number, pass upwards through the back part of the three outer interosseous spaces, between the heads of the dorsal interosseous muscles. On reaching the back of the foot, these small vessels inosculate with the interosseous arteries, branches of the metatarsal artery.
The digital branches, [digitales,] four in number, are named from the order in which they arise from the arch, counting from without inwards, first, second, third, and fourth digital arteries. The first digital branch inclines outwards from the outermost part of the plantar arch, opposite the end of the fourth metatarsal space, to gain the outer border of the little toe. In this course the vessel crosses under the abductor muscle of that toe, and then runs along the outer border of its phalanges, on the last of which it terminates. The second digital branch passes forwards along the fourth metatarsal space, and behind the cleft between the fourth and fifth toes divides into two vessels, which course along the contiguous borders of those toes, and end on the last phalanges; the third digital branch is similarly disposed of on the fourth and third toes; and the fourth on the third and second toes.
Near its point of bifurcation, each digital artery sends upwards through the fore part of the corresponding metatarsal space a small branch, anterior perforating [perforantes ant.] which communicates with the digital branch of the metatarsal artery. . .
The digital arteries of each toe, which, from their relation to the phalanges, are sometimes called collateral, incline one towards the other at their termination and inosculate on the last phalanx near its base, so as to form an arch, from the convexity of which minute vessels pass forwards to the extremity of the toe, and to the matrix of the nail. In this, the ordinary arrangement of the vessels, both sides of the three outer toes, and one side of the second toe, are supplied by branches derived from the plantar arch; whilst, as will presently appear, both the collateral arteries of the great toe, and the inner one of the second, are furnished by the dorsal artery of the foot.
Peculiarities of the plantar arteries. — Some of these will be considered after the description of the anterior tibial artery and its branches in the foot. It may be stated here however, that the posterior perforating branches, which are usually verv small vessels, are sometimes enlarged, and furnish the interosseous arteries on the upper surface of the foot ; the metatarsal branch of the dorsal artery, from which the interosseous arteries are usually derived, being in such cases very small.
From quain's anatomy.