Between the gastrocnemius and the soleus is the plantaris tendon, a long slender slip, which, after crossing between the muscles, runs on the inner side of the tendo Achillis, to its insertion. The belly of this little muscle is under the outer head of the gastrocnemius, close to the origin of which it arises. Authors describe the symptoms attendant upon rupture of this tendon, but the diagnosis of injury to so small and deep-seated an organ must be so uncertain, that we should be much more in clined to refer them to an injury of some of the fibres of the great muscles of the calf, es pecially when we compare the power of the plantaris with that of its tendon, the passive strength of the latter appearing greatly superior to the active force of the former.'" Between the lower part of the tendo Achillis and the tendons of the deep layer of muscles, there is a considerable layer of cellular tissue, con taining fat, and this is often the seat of trouble some chronic inflammation ; and if suppuration follows, the abscess is often very difficult of healing, from the constant movement of the tendon, and the result is a troublesome sinuous ulcer, which can only be healed by keeping the foot entirely at rest.
The deep muscles, bound down in the pos terior interosseal space, by the inter-muscular layer of the aponeurosis, are found lying in this order; the flexor digitorum communis, placed innermost, upon the back of the tibia ; the flexor longus pollicis, on the fibula, and the tibialis posticus between them, and partly con cealed by them. Upon this last muscle are situated the posterior tibial vessels and nerves. As they all of them have to pass nearly behind the inner ankle, the two outermost are gradu ally approaching to the flexor communis, as they descend, till they are nearly in contact one with the other. As all these tendons, either primarily or secondarily, act upon the ankle joint, their action is retained after rupture or division of the tendo Achillis, so that the power of extension of the foot still remains, though in a feeble degree.
The arteries of this region are the posterior tibial and peroneal, and are given off from the termination of the popliteal. The anterior ti bial also has here a course of a few lines, from its origin, till it perforates the interosseous liga ment. The posterior tibial may be considered as the continuation of the trunk of the popliteal. It commences about an inch below the origin of the anterior tibial, and where the popliteal divides into this artery and the peroneal. The course of the posterior tibial may be defined by a line drawn from the middle of the ham, to a spot half an inch behind the inner mal leolus. In this course it is accompanied by two veins, one on either side, also by the poste rior tibial nerve ; in the upper part of the leg, this nerve lies to the inner or tibial side of the artery ; it soon, however, passes over it, and inferiorly it lies to its outer or fibular side.
The posterior tibial artery is covered, in the upper and middle thirds of the leg, by the gas trocnemius and soleus itttirscles, but in the lower third only by the integuments, and by the su perficial and deep fasciae of the leg. In the upper third of its course, this artery rests upon the tibialis posticus muscle, in the middle third upon the flexor digitorum communis, and in the inferior third some fat and cellular membrane separate it from the tibia, and from the internal lateral ligament of the ankle-joint.
In the inferior third of the leg, the posterior tibial artery runs nearly parallel to the inner edge of the tendo Achillis ; between the os calcis and malleolus internus, it lies nearly in contact with the sheath of the flexor digitorum comrnunis.* The only branch of surgical in terest given off by this artery in the leg is the nutritious artery of the tibia, which comes off about its upper third, and in amputation at this part sometimes bleeds freely.
In putting a ligature upon this artery, the difficulties attendant upon the operation vary according to the situation at which we seek for it. It is favourably circumstanced for opera tion in the inferior third of its course, being covered in the two upper thirds by the muscles of the calf. It may require to be tied for a wound in the sole of the foot, or for one behind the inner ankle. In either of these cases the artery may be found and tied with facility be hind the inner malleolus. (See ANKLE-JOINT, REGION or.) When, however, it is deemed de sirable to tie it at the lower third of the leg, it will be readily found by an incision of from two to three inches in length, performed mid way between the inner border of the tibia and the tendo Achillis. After the division of the integuments, the superficial fascia, and the deep fascia, the artery will be met with di rectly under the incision. Its accompanying veins sometimes completely conceal it ; the nerve is here on the fibular side of it.
In case of secondary hemorrhage after this operation, or in case of aneurism of the pos terior tibial artery, forming in consequence of a wound of the artery in this situation, it may be necessary either to tie this vessel higher up in the leg, or to tie the popliteal femoral artery itself; it has been deemed prudent to give the patient the chance of success from the former operation, before having recourse to so severe and hazardous a measure as that of tying the femoral or popliteal artery.