The operation of tying the posterior tibial artery in the middle of the leg will be found much more difficult than either of the other situations mentioned, as this vessel here lies at such a depth from the surface, and is covered by the gastrocnemius and internal head of the solens, which in this situation is attached to the tibia. To expose the artery here, the leg should be bent, the foot extended, and both laid on the outer side. The incision must be of considerable length, not less than four inches, along the inner edge of the tibia. The integuments and fascia being divided, (care being at the same time taken to avoid the saphena vein,) the edge of the gastrocnemius muscle will be exposed ; this will be easily raised and drawn to one side. The soleus must next be divided from its attachment to the tibia, and at the bottom of this incision will be discovered some dense aponeurotic fibres, which are part of the deep fascia of the leg. The muscular fibres in the incision must now be held wide apart, and carefully sepa rated from this deep fascia preparatory to its division, and immediately underneath this fascia lies the artery, with its accompanying veins, one on each side, with the nerve on its inner or tibial side, and here situated about an inch from the edge of the tibia.
On the dead subject this operation is not attended with much difficulty ; in the living, however, the case is very different; the mus cles are then rigid and unyielding, and when the fascia which covers them is divided, they leave their natural situation, and become much elevated, so as to make the situation of the artery appear as a deep cavity, at the bottom of which the vessel is placed. The contraction of the muscles has been found in some cases so great an impediment to the operation, as to require the transverse division of part of the muscle. The operation of cutting directly from behind, through the fibres of the gas troenemius, is obviously still more objection able, from the cause just mentioned.
The second terminating branch of the pop liteal artery is the peroneal. This is situated deeply, along the posterior part of the leg, taking the direction of the fibula ; hence it is sometimes called fibular. It commences about an inch or two below the lower border of the popliteus muscle, after perforating the tibialis posticus at the commencement of its course, and descends, almost perpendicularly, towards the outer ankle. In this course, it lies close upon the fibula, between the flexor proprius pollicis and flexor digitorum communis. On reaching the lower extremity of the interos seous ligament, it divides into two branches, the anterior and posterior peroneal, the first of which passes through the aperture at this part of the interosseous ligament, and both of these run to the outer side of the foot. This artery
is so small and so deeply seated, that its wounds are rare and unimportant. Hence but little has been said of its ligature, which would be very difficult, and could only be per formed at the middle of the external side of the leg. We should then divide the same parts as for the tibial, but on the opposite side, and as it is enveloped in the fibres of the flexor longus pollicis, we must also detach this muscle from the fibula.
Each of these arteries of the posterior region is accompanied by two veins, which fre quently overlap the artery so as to conceal it from view, in the operation of securing it; they are also so adherent to its coats as to occa sion some difficulty in separating them, so as to avoid including them in the ligature, parti cularly where the artery, as in the present in stance, is deep-seated. The best mode of accomplishing this is to insinuate the aneu rismal needle first on one side, and then upon the other, not attempting to bring it. out on the opposite side of the artery, till, by this means, the lateral attachments are separated.
The deep nerve which accompanies the posterior tibial artery is the tibial, and is of considerable size, being the continuation of the trunk of the popliteal. It is situated, at first, to the outer side of the artery, and lower down it runs nearly behind it, and so close to it, that without care it may be injured, included in the same ligature, or even tied for that vessel.
It may not be amiss here to observe on the distinctive marks by which the nerve may be recognized, when passing the ligature under the artery, that besides the most essential, the absence of pulsation, which may occur even to the artery itself from accidental causes, the inexperienced operator will find considerable assistance from the following, viz. the firm, round, cord-like feel of the nerve, while the artery has a flattened yielding feel when pressed between the finger and thumb, and the whitish, somewhat glistening, and promi nent round appearance of the nerve, the artery having a somewhat reddish colour, and a flat tened, thick, and riband-like appearance, as it is raised upon the aneurism needle. When the cut extremities of the two are seen toge ther, after an amputation, of course the round open mouth of the one, and the prominent stump of the other, like a tight packet of thread cut across, are readily recognizable.
The lymphatics of these deep parts accom pany the bloodvessels, and pass to the glands of the ham ; hence diseases occurring in the parts beneath the aponeurosis of the leg exert their influence on the glands of the popliteal space.