THE MATELINAL ILIAC A ItTCRY, (arterin iliaca e.rlemin, Lat.; arti:re iliaquc exterric, Fr. ; portion iliaque de la crurale, Chauss. ; Aussere lliift-pulsadcr, Ger.) is the vessel destined for the supply of the lower extremity, of Ndlich the portion contained within the abdomen, in the iliac region, is denominated the " external " iliac, in contradistinction to the artery of the pelvis, the " internal." It commences at the division of the primi tive iliac artery, at a point intermediate to the body of the last lumbar vertebra, or the sacro vertebral prominence, and the sacro-iliae articu lation, and it terminates at the crural arch, at a point midway between the superior anterior spinous process of the ilium and the spinous process of the pubis,' or at the outer side of the ilio-pectineal eminence of the os innomina tum. The point at which the vessel com mences is not uniform either in all subjects or on the two sides of the same; depending upon the point at which the primitive iliac divides, which is variable, it will be higher or lower, nearer to the vertebra or to the articulation, according to the situation of the bifurcation of that vessel : on the right side of the body the artery commences for the most part nearer to the body of the vertebra than on the left, on which it is of course nearer to the articulation ; hence the artery arising higher upon the former is longer upon that side than upon the latter, the difference in length varying from a quarter to half an inch. The external iliac terminates in the femoral or crural artery, strictly so called ; but the distinction between the two is one only of convenience, inasmuch as they are but different stages of the same vessel ; there appears therefore much propriety in the designation adopted by Chaussier, which, while it recognises the identity of the vessel throughout its course, sufficiently marks the grounds of distinction between its two portions. The external is somewhat smaller than the primitive iliac, but in the adult considerably larger than the internal ; its direction is down ward, outward, and forward, and hence it forms with the primitive iliac a curve convex backward, and seems the continuation of that vessel ; its length is from three to four inches, and during its course it forms one or more curvatures.
Such is the disposition of the vessel in the adult; but in the younger subject it is different in some respects; in the foetus the external iliac is considerably smaller than the internal, and does not seem the continuation of the primitive iliac, which at that epoch is continued into the internal ; the external appearing rather as a branch or_ a smaller division from a trunk common to the other two : after birth the relative disposition of the iliacs gradually changes, until they acquire that of the adult.
The relations of the external iliac artery are as follows : posteriorly, it corresponds through the upper half of its course to the lateral part of the superior aperture of the pelvis; inclining outwards as it descends, it corresponds in its lower half to the os innominatum, and the more perfectly, the nearer it approaches the crural arch, at which part it is placed in front of the bone, crossing it nearly at right angles, and separated from it by an interval occupied by thepsoo-iliac aponeurosis and the psoas muscle.
At its outset the external iliac vein is directly behind the artery, and on its right side, also the commencement of the primitive iliac vein, the artery crossing the junction of the two vessels, on that side, obliquely in its descent ; during the remainder of its course, the vein, though posterior to it, is also internal ; through out the lower half of its course it lies upon the psoo-iliac aponeurosis, supported by the as innominatum, and at first separated from the bone only by the aponeurosis ; but as it pro ceeds separated from it also by the tendon of the psoas parvus when present, and by the inner mar gin of the psoas magnus, it is very near to the as innominatum, external to the ilio-pectineal emi nence, and being here supported by bone, and made steady by its connections it may with certainty be compressed and its circulation perfectly commanded. Internally, the artery corresponds above to the aperture of the pelvis, to its viscera more or less intimately, according to their state of distension or contraction, and also to the small intestines which descend into it ; in the lower half of its course, the external iliac vein, which at its outset is behind or beneath the artery, is internal, though still some what posterior to it ;at the crural arch the artery and vein are nearly upon the same level, being supported by the os innominatuni ; the artery however somewhat anterior to the vein, but as the vein recedes from the arch it inclines less inward than the artery, and at the same time retreats more from the surface; and hence it gradually gets more completely behind the artery until at its junction with the primitive vein it is concealed by it anteriorly.