When the cutis is removed, we expose a stratum of cellular tissue remarkable for its density and toughness, and for the granular fat with which its cells are filled; it lies imme diately under the true skin, and over the plantar fascia. We may here observe that a similar integument, and the same kind of cel lular web under it, is spread over the heel, and, from the peculiarity of its texture, is probably more likely to inflame under the effects of pressure than the skin of other parts of the body ; at any rate, it very frequently does inflame, and even slough, when long subjected to pressure ; and inattention to this point is often the source of great misery in the treatment of fractures and dislocations of the lower extremity. The heel resting upon some hard portion of the apparatus often so torments the patient as to be a serious impedi ment to the successful treatment of the case.
The fascia plantaris demands our particular attention. It is a strong tendinous structure forming a covering to the muscles and impor tant structures of the sole. It is very thick and dense at its posterior part, and becomes thinner, though still of the same consistence, at the anterior part. The cellular web just mentioned strongly adheres to it externally, while the muscles which it covers are not only adherent to its inner side, but many of their fibres arise directly from it. It not only forms a layer of separation between these muscles and the more external parts, but it sends pro cesses of a similar tendinous structure between the principal muscles, which also afford origin to many of their fibres. It divides itself into three portions, one covering each of the three principal groups of muscles found here. These three portions are, however, united behind where they arise in common from the under projecting part of the os calcis, while ante riorly the layer becomes quite incomplete from the subdivision into five slips, each of these again splitting to pass to be fixed into each side of the heads of the metatarsal bones. The situation, structure, and connexions of this fascia, of the dense stratum of cellular tissue, and of the peculiar skin covering this, are highly important to the surgeon. The know ledge of these points teaches why phlegmonous inflammation must be difficult of treatment, and often dangerous in its results, whether it occurs immediately under the skin or under the fascia, but particularly in the latter situa tion, the dense unyielding structure of which prevents the swelling from pressing outward, thus greatly aggravating the pain and irritation, and when matter has formed, equally prevents its pointing outwards, and calls for the early application of the lancet to give it free vent, and thus prevent its spreading along the foot. The structure of the parts just described is, as far as it goes, an objection to the partial ampu tation of the foot recommended by Chopart, wherein the flap is formed from these parts in the sole, together with the muscles and tendons found there. But this objection is by no means fatal to operations upon these parts, which have often been successfully performed, and when they are so, often give a limb much more useful than a wooden one.
We now come to the deep-seated parts of the foot. These consist, 1. of the muscles and tendons; 2. of veins and arteries ; 3. of nerves; 4. of absorbents. The muscles and tendons compose three principal groups des tined to accomplish the movements of the great toe, of the three middle toes, and of the little toe, and according to their destination and use, so is their situation in the sole. On the inner side the abductor, the adductor, the flexor brevis, and tendon of the flexor longus pollicis form a pretty considerable mass, and have a separate slip of the fascia plantaris lying under them, in contact with the most superficial of them, viz. the abductor. On the outer or fibular side of the sole, a similar mass of muscles, but smaller, lie underneath the metatarsal bone of the little toe, composed also of an abductor and a short flexor, while one slip both from the long and short common flexors joins them anteriorly. The space be tween these two masses of muscles is occupied, most superficially, and immediately in contact with the plantar fascia, by the flexor brevis digitorum, next by the tendons of the flexor longus digitorum, accompanied by their acces sories ; posteriorly, the accessories or massy cornea Jacobi Sylvii ; and anteriorly, the lum bricales, while deeper still than all there are the interossei interni.
Amidst this number of small muscles, the plantar arteries take their course in the follow ing manner. The posterior tibial artery, as we have elsewhere seen (vide ANKLE-JOINT, REGIONS or), passing down behind the inner malleolus, gets into the hollow of the os calcis, lying pretty close to this bone, and covered only by the integuments, cellular tissue, and fascia. It now passes between the origins of the adductor pollicis, and in doing so divides into external and Internal plantar. The first of these, which is much the larger of the two, runs in a somewhat semicircular course, first forwards and outwards till it has reached the base of the metatarsal bone of the little toe, and then winds round across the other metatarsal bones, till at that of the great toe it terminates by uniting with the anterior tibial. In this course it runs first between the superficial and deep muscles, viz. first covered by the abductor pollicis, then between the flexor brevis digitorum and the long flexor tendons ; it then becomes more superficial, lying between the flexor digitorum brevis and the abductor minimi digiti; then in crossing back to the inner side of the foot, it runs deep under all the muscles and tendons, except the interossei. Thus this artery forms an arch, called the plantar arch, having its convexity forwards and outwards, its concavity inwards and backwards. The branches which it sup plies in this course are, first, a number of large muscular branches before it reaches the outer side of the foot ; then from the convexity of the inch itself, the digital arteries, one to each metatarsal space, which, dividing at the first joint of the toes, run one on each side of the toe to its termination ; and lastly, those from the upper and inner sides, being generally very insignificant muscular branches and communi cating branches, these last going upwards between the metatarsal bones to anastomose with • the metatarsal branches of the anterior tibial artery. It is right, however, to state that in this, as in every other part of the arterial system, great variety is occasionally found. The internal plantar artery is a com paratively small artery, merely going to supply the muscles and integuments of the great toe, and for this purpose passes forwards along the under and inner side of the tarsus, covered by the abductor pollicis as far as the first phalanx of the great toe, where it divides into several branches, supplying both sides of the great toe, and the inner side of the second. The veins which accompany the plantar arteries are, like all deep-seated veins, two in number, one on each side of the artery, and they terminate in the hollow of the os calcis by forming the posterior tibial veins. The plantar arteries are accompanied also in their course by corre sponding nerves, the termination of the poste rior tibial nerve, which divides in the hollow of the os calcis. The internal plantar nerve, contrary to the order of the arteries, is the larger of the two ; it runs in company with the inner plantar artery, and sends branches to the three inner toes, and to the inner side of the fourth, while the external plantar nerve running the course of the corresponding artery is dis tributed only to the filth toe and outer side of the fourth. The lymphatics of the sole of the foot, like the rest of this system, are com posed of a superficial and a deep set, the former collecting from all parts towards the inner ankle; the latter accompanying the tar arteries and veins, and passing up also with them behind the inner ankle, go with the tibial veins to the ham. There are several synovial bursa' in this region which it is necessary here to mention. They are surrounding the tendons as they pass into the sole along the hollow of the os calcis, viz. the flexor longus pollicis and flexor longus digitoruin. Their anatomical description has been already given (see ANKLE, REGION OF). Another synovial sheath is surrounding the tendon of the pemneus longus as it obliquely crosses the sole to its insertion. This bursa! cavity is situated close upon the bone, and under the principal ligaments.