distributed to the joint in company with the inferior external articular artery.

Fig. 238.

The POPLITEAL ARTERY, Fig, 238 (1), is a continuation of the femoral. It commences at the lower end of the canal formed by the tendons of the adductores longus and magnus, and passes downwards and outwards, first over the femur, then the posterior ligament of the joint, and lastly the aponeurosis, which covers the popliteal muscle, at the lower border of which, it divides into the posterior tibial and peroneal or fibular. At first, it is to the inner side of the median line of the limb, but gets into it as it descends behind the joint. The popliteal vein, Fig. 240 (5), lies behind and a little to the outer side of it above the joint, but directly behind it in the rest of its course. The coats of this vein are very thick, so that when cut it sometimes gapes, and might then be mistaken for the artery. It also adheres very closely to the artery, which should be borne in mind, whenever it is necessary to place a ligature on the latter. The lower part of the artery is partly covered by the heads of the gastrocnemius and the plantaris; the popliteal nerve also crosses this part of it from the outer to the inner side. It has on the sides of it the different parts which form the boundaries of the popliteal space, which are specified above. The relations of the popliteal artery to the knee-joint are interesting, and should be carefully observed. When one limb is placed across the other, as in sitting, the pulsations of the artery are distinctly seen in the movements of the foot, so that the beats of the heart can be counted as accurately, by observing the movements of the foot with the legs crossed, as by placing the fingers on the radial artery in the wrist. There are eight branches given

A VIEW OF THE ARTERIES

IN THE POPLITEAL SPACE,

RIGHT LEG. - 1. Popliteal artery. 2. Internal gastroc

nemial artery. 3. External gastrocnemial artery. 4, 5. the substance of the muscle.

Division of these arteries in.

off from the popliteal artery, which require to be noticed. Six of these are articular branches, and two are muscular.

The superior internal articular arteries, consist of two. One of these is sometimes called the great anastomotic artery, Fig. 213 (20, 21), of the knee. It may arise from the femoral artery as it is passing through the tendinous sheath to become the popliteal; or it may have its origin still higher up. After perforating the adductor magnus, it divides into several branches. One of these passes downwards behind the sartorius muscle, in company with the internal saphenous nerve; another one passes downwards through the substance of the vastus internus muscle, and, reaching the inner border of the tendon of the quadriceps extensor muscle, just above the pa tella, where it becomes subcutaneous, and crossing transversely to the outer side, along the upper border of the patella, it anastomoses with the superior external articular branch. It sends branches to the anterior surface of the patella. One or two branches are distributed principally to the periosteum on the inner and anterior surface of the femur. One of these sometimes takes the place of the next artery to be described, or terminates by anastomosing with it.

The lower superior internal articular artery, Fig. 239 (4), arises just above the internal condyle, passes horizontally inwards and around the condyle, to gain its anterior surface. It sends branches to the patella and to the synovial membrane, and other branches to the integument, and to anastomose with the preceding branch and one or two of the other articular branches.

The superior external articular artery, Fig. 239 (5), arises just above the external condyle, and, passing under the biceps flexor muscle, divides into several branches; some of which are muscular, and others are periosteal. The former are ascending branches, and go to the biceps and the quadriceps extensor muscles. The latter are found ramifying on the condyle and the anterior surface of the lower part of the femur, and also on the outer part of the patella. They also anastomose freely with the other articular branches.

The inferior external articular artery, Fig. 239 (8), arises oppo site the articulation, and passing horizontally outwards in a line corresponding to the joint, and beneath the tendon of the biceps and the external lateral ligaments, divides into au ascending, a transverse, and a descending branch. The first

Fig. 239.

passes upwards along the outer border of the patella, and anastomoses with the superior external articular artery. The second, passing transversely below the patella and between the ligamentum patellæ and the joint, anastomoses with the inferior internal articular artery; it also sends small branches to the fat and areolar tissue beneath the ligamentum patellæ. The last one anastomoses with the anterior recurrent tibial, a branch of the anterior tibial artery.

The inferior internal articular artery, Fig. 239 (7), arises opposite to the preceding artery, and passing downwards and inwards around the internal tuberosity of the head of the tibia, and beneath the tendons of the muscles which form the inner hamstring, and the internal lateral ligament of the kneejoint, it turns upwards towards the patella. It anastomoses with the preceding artery beneath the ligamentum patellæ, and also with the superior internal articular arteries.

The middle articular artery, or the azygos artery, Fig. 239 (6), arises from the forepart of the popliteal artery, and passes directly through the posterior ligament, to be distributed to the synovial membrane, the areolar tissue, and the crucial ligaments within the knee-joint; some of its branches penetrate the lower extremity of the femur.

A VIEW OF THE ARTERIES ON THE BACK OF THE RIGHT LEG. THE MUSCLES HAVE BEEN REMOVED SO AS TO DISPLAY THE VESSELS IN THEIR WHOLE LENGTH.-1.. The popliteal artery, cut off so as to show the articular arteries. 2. Lower end of the same artery on the popliteus muscle. 3. Point of bifurcation into the posterior tibial and peroneal. 4. Lower superior internal articular artery. 5. Superior external articular artery. 6. Middle articular artery. 7. Inferior internal articular artery. 8. Inferior external articular artery. 9. Branch to the head of the soleus muscle. 10. Origin of the anterior tibial artery. 11. Origin of the posterior tibial artery. 12. Point where it passes behind the internal annular ligament to become the plantar. 13, 14, 15. Muscular branches. 16. Origin of the peroneal artery. 17, 17. Muscular branches. 18, 18. Anastomosis of the posterior tibial and peroneal arteries near the heel. 19. Muscular branch from the anterior tibial.

Instead of one middle artery, there may be several smaller ones going to supply the same parts. Like those which have been described above, it may take its origin from some one of the other articular arteries; all the arteries around the kneejoint vary more or less in their origin, and also in their size. The patella is the centre of their anastomotic connections.

The gastrocnemial arteries, Fig. 238 (2, 3), arise from the back of the popliteal artery, nearly opposite the articulation, and passing downwards are distributed, one to each of the heads of the gastrocnemius. They are usually larger than the articular branches. They correspond to muscular branches given off from the popliteal artery, above the knee-joint, to be distributed to the muscles in the lower part of the thigh.

SECT. IV.-DISSECTION OF THE POSTERIOR AND THE INNER PART OF THE LEG.

To dissect the posterior part of the leg, the integument may be removed by making an incision from the popliteal space along the median line to the heel, and thence along both the inner and outer borders of the plantar surface of the foot to a point on each side below the malleolus. From this incision the skin can be reflected externally and internally sufficiently to expose all the parts in this region. The foot should be flexed on the leg so as to make the fascia, as well as the muscles to be dissected, tense. Although it is conve nient to describe, at this time, the parts which correspond to the subcutaneous surface of the tibia, it is not necessary that the integument which covers this surface should be removed in connection with that on the back of the leg. It is better that the student should dissect specially for the internal saphenous vein and nerve, as there is nothing else of any importance on the inner part of the leg. The vein, if injected, or filled with blood, is easily found and traced; but it is much more difficult to find the nerve, unless it was preserved when the dissection of the anterior part of the thigh was made. To dissect them on the leg, it is immaterial whether the subject be placed on the back or on the face; if on the back, the integument can be reflected from behind forwards, and the dissection can be made in connection with the back of the leg.

Having reflected the integument from the incision made in the median line to a line corresponding to the fibula and external malleolus on the outer side, and to the inner angle of the tibia and internal malleolus on the inner side, the cutaneous vessels and nerves should be examined. If it be decided to dissect the internal saphenous nerve and vein in connection with the back of the leg, then the internal flap must be raised as far as the anterior angle or spine of the tibia. Special care is requisite in raising the integument that the superficial fascia be left in order that the cutaneous vessels and nerves may not be injured or destroyed before they have been dissected.

There are no arteries in the superficial fascia that require particular notice.

The veins to be examined in the superficial fascia are the two saphenous, external and internal. The latter was dissected in the upper part of its course in connection with the thigh, and the former, with the popliteal space. They both commence on the dorsum of the foot, and are subcutaneous to within a very short distance of their termination, the one in the femoral, and the other in the popliteal vein. They communicate freely with each other on the leg, and sometimes the external joins the internal instead of the popliteal. They contain very few valves, which may contribute to the forma tion of varix, and also tend to prevent the obliteration of the veins, as they can, in the absence of valves, more readily empty themselves by means of collateral branches; the internal has from two or three to six valves, and the external only two.

The INTERNAL SAPHENOUS VEIN, Fig. 208, arises by the internal dorsal vein of the foot, passes back wards and upwards on the inner part of the dorsum, and in front of the anklejoint to the anterior part of the internal malleolus, and thence along the inner angle of the tibia to the internal and posterior part of the knee-joint. In this part of its course it receives branches from both sides of it. In the foot it communicates with the deep plantar vein, and receives the superficial veins of the inner part of the plantar portion of the foot, including the internal calcaneal veins. Sometimes the lastnamed veins form a trunk which passes upwards behind the internal malleolus, and there unites with the saphenous.