The vessel which supplies the lower extremity forms a continuous trunk from the point of division of the common iliac artery down to the lower border of the popliteus muscle, where it divides into the anterior and posterior tibial arteries ; but though thus continued as a single trunk different parts of the vessel have received different names, taken from the anatomical regions through which they pass. Whilst within the pelvis, it is named iliac; in the upper two-thirds of the thigh, femoral ; and thence to its termination, popliteal. These divisions, however, are artificial, and are intended merely to facilitate reference to the vessel in different situations.

The external iliac artery [a. iliaca externa, French : Artère iliaque externe], larger, except in the fetus, than the internal iliac artery, is placed within the abdomen, and extends from the division of the common iliac to the lower border of Poupart's ligament, where the vessel entering the thigh, assumes the name femoral. Descending obliquely outwards, its course through the abdominal cavity would be marked by a line drawn from the left side of the umbilicus to a point midway between the anterior superior process of the ilium and the symphysis pubis. This line, however, would also indicate the direction of the common iliac artery, from which the external iliac is directly continued.

Placed within the abdominal cavity, the vessel is covered by the peritoneum and intestines. It lies along the outer margin of the true pelvis, resting on the psoas muscle along its inner border. The artery, however, is separated from the muscle by the fascia iliaca,, to which it is bound, together with the external iliac vein, by a thin layer of membrane.

The external iliac vein lies at first behind the artery with an inclination to its inner side; but as both vessels approach Poupart's ligament at the fore part of the pelvis, the vein is on the same plane with the artery to its inner side, being borne forwards by the bone. At. a short distance from its lower end the artery is crossed by the circumflex iliac vein. Lymphatic glands are found resting upon the front and inner side of the vessel, and the spermatic vessels descend for some space upon it. A branch of the genito-crural nerve crosses over it just above Poupart's ligament.

The external iliac artery supplies some small branches to the psoas muscle and to the neighboring lymphatic glands, and two other branches of considerable size, named the epigastric and the circumflex iliac, which are distributed to the walls of the abdomen.

The usual number of the two principal branches may be increased by the separation of the circumflex iliac into two branches; or by the addition of a branch usually derived from another source, as the internal circumflex artery of the thigh, or the obturator artery.

On the contrary, the branches are now and then diminished in number by the transference of the epigastric or the circumflex iliac artery to another trunk, which is commonly the femoral.

From Quain's anatomy.