The limb being laid as before on the outside, and slightly bent, the skin shaved and the pulsation of the artery detected, an incision (Plate I. fig. 6) must be made from the lower edge of the sartorius muscle just as it crosses the vessel, along the course of the vessel, avoiding if possible the internal saphena vein. The sartorius when exposed must be drawn inwards. The fibrous canal filling the interspace between the abductor magnus and vastus internus is then recognised, and must be fairly opened; the artery is now seen lying in it, and over the vein which is posterior to it, but projects slightly on its outer side; the internal saphenous nerve is lying on the artery. The needle is best passed from without inwards so as to avoid the vein. The anastomotica magna is sometimes a large trunk, and has been mistaken for the femoral in this situation, and tied instead of it. LIGATURE OF THE POPLITEAL.--This operation is now hardly ever performed for aneurism, ligature of the superficial femoral having quite superseded it, and it is very rarely required for wounds, from the manner in which the vessel is protected by its position. Before the invention of the Hunterian principle of ligature at a distance, the old operation for popliteal aneurism consisted in cutting into the space, clearing out the contents of the aneurismal sac, and tying both ends of the vessel; from the depth of parts and the close connection of the popliteal vein, this operation was very rarely successful, and is now quite given up. If the vessel is wounded the bleeding point is the object to be aimed at, and is generally sufficient guide. In cases of hæmorrhage for suppuration of an aneurismal sac, it might possibly be advisable, and there are certain cases of rupture of the artery, without the existence of an external wound, in which attempts have been made to save the limb by tying the vessel.[10] From the complexity of the parts, the numerous tendons, veins, and nerves crowded together in a narrow hollow, and chiefly from the great depth at which the artery lies, any attempt at ligature is very difficult. It is least so at the lower angle of the space, where, between the heads of the gastrocnemius, the vessel comes more to the surface, but is still overlapped by muscle.