LIGATURE OF EXTERNAL ILIAC.--_Anatomical Note._--This artery extends from the bifurcation of the common iliac to the centre of Poupart's ligament, where it leaves the abdomen, passing under the ligament, and becomes the common femoral. Its upper extremity is thus not always constant, varying in position from the sacro-lumbar fibro-cartilage to the upper end of the sacro-iliac synchondrosis, or even a little lower down. Thus, though the position of the lower end is at a fixed point, the artery varies in length. In an adult male of moderate stature it is from three and a half to four inches in length. On the surface of the abdomen the position of this vessel would be indicated by a line drawn from about an inch on either side of the umbilicus to the middle of the space between the symphysis pubis and the crest of the ilium. Its relations to neighbouring parts are as follows:--The peritoneum lies _in front_ of it, separated from it only by a subperitoneal layer of loose fascia, in which the artery and vein lie, which varies much in consistence and amount, and which occasionally gives a good deal of trouble in the operation of ligature. Near its origin it is sometimes crossed by the ureter, and near its termination the genito-crural nerve lies on it. The spermatic vessels cross it, and occasionally a quantity of subperitoneal fat marks its course. _Externally._--The fascia-iliaca and some fibres of the psoas muscle separate it from the anterior crural nerve, which lies outside of the vessel, and at a somewhat deeper level, hidden amid the fibres of psoas and iliacus. _Internally._--The external iliac vein lies on the same plane, and to the inner side of the artery, at Poupart's ligament, on both sides of the body. As we trace it upwards we find that on the left side it lies internal to the artery in its whole course, while on the right side it becomes posterior to the artery as it approaches the bifurcation of the common iliac. Lastly, just before the vessel reaches Poupart, the circumflex iliac vein crosses it from within outwards. _Branches._--The two large branches to the wall of the abdomen, the epigastric and the circumflex iliac, rise a few lines above Poupart's ligament. Their position is unfortunately apt to vary upwards, to the extent of an inch and a half or even two inches, and they are important, as, besides being liable to be cut during the operation, their position very materially modifies the prognosis, as, if too high up, they interfere with the proper formation of the coagulum.