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COMMENTARY ON PLATES 65 & 66.
The popliteal artery, F, Plate 66, being the continuation of the femoral, extends from the opening in the great adductor tendon at the junction of the middle and lower third of the thigh, to the point where it divides, in the upper, and back part of the leg, at the lower border of the popliteus muscle, L, into the anterior and posterior tibial branches. In order to expose the vessel through this extent, we have to divide and reflect the heads of the gastrocnemius muscle, E E, and to retract the inner flexors. The popliteal artery will now be seen lying obliquely over the middle of the back of the joint. It is deeply placed in its whole course. Its upper and lower thirds are covered by large muscles; whilst the fascia and a quantity of adipose tissue overlies its middle. The upper part of the artery rests upon the femur, its middle part upon the posterior ligament of the joint, and its lower part upon the popliteus muscle. The popliteal vein, G; adheres to the artery in its whole course, being situated on its outer side above, and posterior to it below. The vein is not unfrequently found to be double; one vein lying to either side of the artery, and both having branches of communication with each other, which cross behind the artery. In some instances the posterior saphena vein, instead of joining the popliteal vein, ascends superficially to terminate in some of the large veins of the thigh. Numerous lymphatic vessels accompany the superficial and deep veins into the popliteal space, where they join the lymphatic bodies, which here lie in the course of the artery. The branches derived from the popliteal artery are the muscular and the articular. The former spring from the vessel opposite those parts of the several muscles which lie in contact with it; the latter are generally five in number--two superior, two inferior, and one median. The two superior articular branches arise from either side of the artery, and pass, the one beneath the outer, the other beneath the inner flexors, above the knee-joint; and the two inferior pass off from it, the one internally, the other externally, beneath the heads of the gastrocnemius below the joint; while the middle articular enters the joint through the posterior ligament. The two superior and inferior articular branches anastomose freely around the knee behind, laterally, and in front, where they are joined by the terminal branches of the anastomotic, from the femoral, and by those of the recurrent, from the anterior tibial. The main vessel, having arrived at the lower border of the popliteus muscle, divides into two branches, of which one passes through the interosseous ligament to become the anterior tibial; while the other, after descending a short way between the bones of the leg, separates into the peronaeal and posterior tibial arteries. In some rare instances the popliteal artery is found to divide above the popliteus muscle into the anterior, or the posterior tibial, or the peronaeal. The two large muscles, (gastrocnemius and soleus,) forming the calf of the leg, have to be removed together with the deep fascia in order to expose the posterior tibial, and peronaeal vessels and nerves. The fascia forms a sheath for the vessels, and binds them close to the deep layer of muscles in their whole course down the back of the leg. The point at which the main artery, F, Plate 66, gives off the anterior tibial, is at the lower border of the popliteus muscle, on a level with N, the neck of the fibula; that at which the artery again subdivides into the peronaeal, P, and posterior tibial branches, O, is in the mesial line of the leg, and generally on a level with the junction of its upper and middle thirds. From this place the two arteries diverge in their descent; the peronaeal being directed along the inner border of the fibula towards the back of the outer ankle; while the posterior tibial, approaching the inner side of the tibia, courses towards the back of the inner ankle. The gastrocnemius and soleus muscles overlie both arteries in their upper two thirds; but as these muscles taper towards the mesial line where they end in the tendo Achillis, V V, Plate 65, they leave the posterior tibial artery, O, with its accompanying nerve and vein, uncovered in the lower part of the leg, except by the skin and the superficial and deep layers of fasciae. The peronaeal artery is deeply situated in its whole course. Soon after its origin, it passes under cover of the flexor longus pollicis, R, a muscle of large size arising from the lower three fourths of the fibula, N, and will be found overlapped by this muscle on the outer border of the tendo Achillis, as low down as the outer ankle. The two arteries are accompanied by venae comites, which, with the short saphena vein, form the popliteal vein.