The artery is covered by peritoneum, upon its inner side through a considerable part of its course ; above the membrane covers it com pletely ; but as it descends the extent becomes less in consequence of the ascent of the vein ; which thus gradually intervenes between the artery and the membrane, and removes the latter from it altogether in the lower part of its course. When the primitive iliac divides at a high point, the ureter descends into the pelvis internal to the external iliac immediately after its origin ; this occurs more frequently upon the right side than the left. Beneath the perito neum the artery is covered by an investment, of which presently again, attaching it superiorly to the peritoneum and inferiorly to the vein.
Externally the artery corresponds through its entire course to the psoas magnus muscle, but it is separated from it by the psoo-iliac fascia, to which it is connected by its immediate invest ment ; the relation of the artery and the muscle are, however, somewhat different at the upper and lower parts of the vessel's course; above, the artery does not lie upon the muscle, but rests against its inner side along its anterior part, while inferiorly it lies upon the inner margin of the muscle at the same time that it rests against it externally.
The genito-crural nerve is situate along the outer side of the artery ; this nerve, long and slender,a branch of the lumbar plexus, descends upon the psoas, extenal to the artery, and at first at a little distance from it ; as it proceeds, it approaches thevessel ,and lies close to itenveloped in the fascia propria; at the lower part of its course its genital branch frequently passes in front of the artery. The anterior crural vein is also external to the artery ; but it is considerably posterior to it, separated from it by the outer margin of the psoas, between which and the iliacus it lies, and also by the fascia iliaca, which covers it ; the nerve is about half an inch from the artery at the crural arch ; as it recedes from the arch the distance increases.
In front, the artery is covered immediately by a cellular investment, formed by the sub peritoneal cellular structure—the fascia propria —upon the posterior wall of the iliac fossa ; this encloses both the artery and the vein and at the same time connects them ; it varies in its condition according to the subject, in some it appeals a dense, but still cellular expansion, in others from the deposition of fat it forms an adipose stratum, which however still presents a more condensed character in immediate con tact with the vessels ; it adheres closely to the surface of the fascia iliaca upon either side of the vessels and thus attaches them to it ; it is prolonged upward upon the primitive iliac vessels, and helow, it ascends between the peritoneum and the fascia transversalis upon the anterior abdominal wall ; upon the primi tive iliac it is very thin and proportionally weak ; but as it descends it increases in thick ness and strength until at the lower part of the external iliac. It forms a stratum of some
thickness and considerable resistance, deserving of much attention in a practical point of view ; there are imbedded in it immediately above the crural arch, and superficial to the artery, one or more lymphatic glands; the genito-criiral nerve also descends enclosed in this structure, at the outside of the artery. Beneath the investment, and immediately above the crural arch, an ex pansion of limited extent, presenting frequently a true fibrous or aponeurotic character, arises from the front of the vessels, and passing forward becomes identified with the fascia transversalis upon its internal surface; thus connecting the vessels to the anterior part of the superior aperture of the femoral sheath, and closing the interval between these parts, which otherwise would be unguarded.
In the second place the artery is covered anteriorly through about four-fifths of its course by the peritoneum of the iliac fossa ; in the inferior fifth, i. e., for from half to three-fourths of an inch immediately above the crural arch, the membrane passing from the front of the artery to the anterior wall of the abdomen leaves the iliac artery uncovered ; and hence the practical inference that the external iliac artery may be tied without disturbing the peritoneum.
Beneath the peritoneum the artery is crossed at the inferior part of its course by the sper matic vessels, and at the superior, upon the right side very frequently by the ureter.
Thirdly, the viscera of the iliac fossa on the one hand, or of the pelvis on the other, ac cording to circumstances, cross or overlap it ; on the right, the ccecum and the termination of the ileum ; on the left, the sigmoid flexure and the commencement of the rectum, and on both sides the small intestines are placed in front of it. And when the viscera of the pelvis become distended and rise from the cavity they overlap it from that side.