Lying between Poupart's ligament and the innominate bone are a number of structures of surgical importance. The space is rougftly triangular in shape, bounded above by Poupart's ligament, externally by the anterior edge of the ilium, and internally by the horizontal ramus of the pubis, ilio-pectineal eminence, and upper margin of the acetabulum, and is subdivided into an outer oval muscular compartment, and an inner compartment roughly triangular, containing the vessels, by the ilio-pectineal ligament. This ligament is formed of a band of fascia lata, which extends from the deep surface of Poupart's ligament, just external to the artery, to the ilio-pectineal eminence.

The muscular compartment contains the ilio-psoas muscle, the iliacus portion being the more external, and the anterior crural nerve lying in the groove between the iliac and the psoas portions. Then, internal to the ilio-psoas and in the inner compartment, lie the vessels in their sneatfl, the artery being external to the vein, while internal to the vein is the crural canal. The vessels, together with the termination of the long saphenous vein, the anterior crural nerve, crural branches of the genito-crural nerve, and the femoral lymphatic vessels and glands, lie embedded in some loose fatty tissue in a prismatic sulcus, formed by the ilio-psoas on the outer, and the adductor longus and pectineus on the inner side.

The femoral sheath, composed of fascia transversalis in front and fascia iliaca behind, invests the vessels for a distance of about 1½ inches beyond Poupart's ligament, and is divided by slight septa into three compartments, of which the outer contains the artery, the middle the vein, and the internal forms the crural canal. The latter contains some fatty tissue, and one or two lymphatic glands and lymphatic vessels.

The femoral artery lies midway between the anterior superior spine and the symphysis, and is very superficial. It is therefore easily compressed, immediately under Poupart's ligament against the subjacent pubis and hip capsule, and toward the apex of Scarpa's triangle against the shaft of the femur, which lies rather to its outer side. On the other hand, the vessel is liable to injury, which sometimes causes arteriovenous aneurism, when both vein and artery are involved, and it has been opened by ulcerative processes. The common femoral is not infrequently the seat of aneurism, the exposed position and the relationship to the hip-joint exposing it to injury, while it soon breaks up into two large trunks.

The line of the femoral artery in the thigh is from a point midway between the anterior superior spine and the symphysis to the adductor tubercle, when the limb is slightly flexed and rotated outwards. If this line be divided into three equal portions, the first represents so much of the artery as lies in Scarpa's triangle, and the second that which lies in Hunter's canal. The common femoral artery may be ligatured just below Poupart's ligament, or the superficial femoral at the apex of the triangle, the bifurcation taking place about 1½ inches below Poupart. The common femoral is not often ligatured, as gangrene from want of blood-supply is apt to be caused. The limb having been adducted and rotated outwards, and the line of the artery noted, a vertical incision, commencing over Poupart's ligament and extending down some 3 inches, is made through skin, fascia, and fascia lata, the femoral sheath exposed, the arterial compartment opened, and the ligature passed from within outwards. Collateral circulation is established through the gluteal, sciatic, and obturator of the internal iliac, and the deep circumflex iliac of the external iliac, with branches of the profunda, and by the internal pudic of the internal iliac, with the superficial and deep external pudic of the common femoral. The profunda, or deep femoral artery, is given off about 1½ inches below Poupart, and it in turn gives off external and internal circumflex, and perforating branches.

The superficial artery is much more frequently ligatured at the apex of Scarpa's triangle, the circulation being maintained by the profunda and its branches. The limb being placed as above, a 3-inch incision is made in the course of the artery, commencing about 2½ inches below Poupart, through skin, fascia, and fascia lata, the long saphenous vein being avoided if near the incision. The sartorius muscle is now drawn outwards, the sheath of the vessels exposed and opened, the internal cutaneous branch of the anterior crural nerve being drawn to one side, and the vessel ligatured. The vein is here a posterior relation, and the long saphenous nerve and nerve to the vastus internus are external relations. The collateral circulation is maintained by the above-mentioned branches of the iliacs with the profunda branches, and in addition by branches of the profunda with the popliteal and its branches.

A roughly applied tourniquet may cause phlebitis of the femoral vein (and neuralgia of the anterior crural nerve). Phlebitis is said also to have been caused by violent flexion of the thigh. A slight dilatation of the upper part of the femora] vein overlapping the crural canal is not infrequent, and, giving an impulse on coughing, may lead to a diagnosis of femoral hernia.

The long saphenous vein is sometimes varicosed close up to the saphenous opening, and is not infrequently ligatured a little below this point in severe cases of varicose veins of the leg. It is said that this operation has been followed by thrombosis of the femoral vein, and even of the external iliac vein. The anterior crural nerve may be affected by superficial injuries, and sometimes in psoas abscess. The genito-crural nerve supplies the cremaster muscle and also the skin of Scarpa's triangle. Irritation of the skin in this region causes retraction of the testicle, especially in children, and this reflex is used to test the condition of the second lumbar segment of the cord.