POPLITE AL REGION, and POPLI TEAL ARTERY. — The term POPLITEAL REGION is applied to that portion of the lower extremity which occupies the bend of the knee, and includes also the poste rior surface of the thigh, as high as the junction of its middle and lower thirds, and the back part of the upper fourth of the leg : — by its muscular boundaries this region is distinctly defined, and is of a diamond shape, but it is by no means so accurately limited when examined with reference to its surface. The external form of the popliteal region differs materially in the flexed and extended position of the leg ; in the latter case, it has somewhat of an oval outline, the longest dia meter, which is in the vertical direction, greatly exceeding the transverse : the greatest transverse breadth is at the bend of the knee joint. The surface presents an elongated rounded projection, which is received above between two narrow ridges diverging from each other as they are traced downwards ; these latter are produced by the stretching of the skin over the tendons of the hamstring muscles, and are rendered still more distinct by a more or less deep groove, which sepa rates them on either side from the general convexity of the region ; inferiorly, the con vexity of the surface passes off insensibly to the calf of the leg : these charactus are more marked in the strong and muscular. When the leg is bent upon the thigh, the roundness of the upper part of the region is lost, and gives place to more or less of a depression or pit between the still projecting ridges produced by the hamstring muscles ; this depression is popularly known as the hollow of the ham.
The popliteal region is scooped out into a deep, narrow, diamond-shaped cavity, to which in the following description the term " popli teal space " will be applied ; it is situated between the diverging hamstring muscles and the converging heads of the gastrocnemius, and is broader above the knee-joint than be low ; it is filled up by a considerable quantity of fat with areolar tissue, and traversed by the popliteal vessels and nerves ; the semi tendinosus and semimembranosus muscles on the inner side, and the biceps flexor cruris on the outer, bound this space laterally and above ; the two heads of the gastrocnemius with the plantaris muscle form its lateral boundaries below ; anteriorly it is bounded by the posterior surface of the femur, the knee-joint or rather its posterior ligament, and the popliteus muscle, and is closed in posteriorly or superficially by a strong fascia and the skin : it may be as well to mention, that in dissecting the popliteal space we are looking at it from behind, so that the term superficial relates to its posterior aspect.
Before describing the contents of the space, it will be necessary to consider more at length the structures which constitute its boundaries.
The skin and subcutaneous areolar tissue present no very remarkable features for exami nation ; the former is marked at the bend of the joint by a few transverse furrows, which are obliterated when the leg is fully extended ; it is smooth and adherent to the subjacent tissue. This latter differs in no respect from the same structure elsewhere ; it contains a variable amount of fat, and is traversed above by a few filaments from the posterior cuta neous nerve of the thigh, and below, though not invariably, by the posterior saphena vein. This superficial vessel begins, by small branches, at the outer side of the foot, passes behind the outer malleolus, and crosses ob liquely to the middle line of the leg, then ascends vertically upon the aponeurosis, which it frequently perforates before reaching the popliteal region, passes into the space between the heads of the gastrocnemius to terminate in the popliteal vein ; it occasionally sends upwards a branch upon the fascia lata, which, winding round the inner side of the thigh, joins the saphena major vein. The commu nicans tibialis nerve courses with this vein, which it closely accompanies at the lower part of the leg, but is separated from it in the popliteal region by being buried between the heads of the gastrocnemius. The posterior saphena vein is liable to become varicose, but less frequently so than the saphena major : this circumstance is of course readily accounted for by the difference of length and size be tween the two.