For the first two inches or two inches and a half of its separate existence, the superficial femoral lies in Scarpa's triangle, covered, as we said, only by skin and fascia. This triangle is formed by the sartorius and adductor longus muscles which meet at its apex, and by Poupart's ligament, which defines its base. The artery lies almost exactly in the centre of the space, and at the apex is covered by the sartorius muscle. The spot where it goes under the sartorius is the one selected for the application of the ligature. The femoral vein lies to the inner side of the femoral artery in this triangle, but their mutual relations vary with the portion of the limb; for, on the level of Poupart's ligament, the artery and vein lie side by side on the same plane, but in different compartments of their sheath; as the artery dives below the sartorius, the vein is still on the inside, but on a plane slightly posterior; while, by the time they reach Hunter's canal, the vein has got completely behind the artery. The separate compartments of the sheath in which the vessels lie are much less marked as the vessels go down the limb, the septum between the artery and the vein being in most cases very ill marked, even at the level where the ligature is applied. The anterior crural nerve, which on the level of Poupart's ligament lay outside of the artery and on a plane somewhat posterior, has divided into numerous branches before it reaches the point of ligature. One of its branches requires to be mentioned, and may sometimes be noticed and avoided during the operation, namely the internal saphenous nerve, which, first lying external to the artery, crosses it in front, reaching its inner side just before it enters Hunter's canal, where it leaves the vessel accompanying the anastomotica magna branch. OPERATION OF LIGATURE OF THE FEMORAL--SCARPA'S SPACE.--The patient being placed on his back, and being brought very thoroughly under chloroform, the knee of the affected limb should be bent at an angle of about 120°, and supported on a pillow. Having previously ascertained the angle of junction of the sartorius and adductor, the surgeon should make an incision (Plate I. fig. 5) just over the pulsations of the vessel, in the middle line of the space, having its lower end quite over the sartorius muscle, and its upper one, at a distance from two and a half to three and a half inches, varying according to the amount of fat and muscle. The saphena vein can generally be recognised, and is almost always safe out of the way of this incision at its inner side.