The main artery of the lower limb may be exposed and tied in any part of its course from the aorta to the popliteal space. But the situation most eligible for performing such an operation depends of course upon circumstances, both anatomical and pathological. If an aneurism affect the popliteal part of the vessel, or if, from whatever cause arising, it be found expedient to tie the femoral above this part, the place best suited for the operation is that where the artery, W, first passes under cover of the sartorius muscle. [Footnote] For, considering that the vessel gives off no important branch destined to supply any part of the thigh or leg between the profundus branch and those into which it divides below the popliteal space, the arrest to circulation will be the same in amount at whichever part of the vessel between these two points the ligature be applied. But since the vessel in the situation specified can be reached with greater facility here than elsewhere lower down; and since, moreover, a ligature applied to it here will be sufficiently removed from the profundus branch above, and the seat of disease below, to produce the desired result, the choice of the operator is determined accordingly. The steps of the operation performed at the situation W, where the artery is about to pass beneath the sartorius, are these: an incision of sufficient length--from two to three inches--is to be made over the course of the vessel, so as to divide the skin and adipose membrane, and expose the fascia lata, through which the inner edge of the sartorius muscle becomes now readily discernible. A vein (anterior saphena) may be found to cross in this situation, but the saphena vein proper is not met with, as this lies nearer the inner side of the thigh. The fascia having been next divided, the edge of the sartorius is to be turned aside, and now the pulsation of the artery in its sheath will indicate its exact position. The sheath is next to be opened, for an extent sufficient only to carry the point of the ligature-needle safely around the artery, care being taken not to injure the femoral vein, which lies close behind it, and also to exclude any nerve which may lie in contact with the vessel. [Footnote: This is the situation chosen by Scarpa for arresting by ligature the circulation through the femoral artery in cases of popliteal aneurism. The reasons stated in the text are those which determine the surgeon to perform the operation in this place in preference to that (the lower third of the thigh) where Mr. Hunter first proposed to tie the vessel.]