The obstruction to the course of the opera tion caused by the protrusion of the viscera is to be expected ; in that of Mott it is described as very great, while no mention is made of it in Crampton's. This difference was probably the consequence of the difference in the site of the wounds. The separation of the artery and vein is more easily effected than in the case of the external aloes, because their investment is less thick and resisting.
The diversity presented by the arteries of the opposite sides suggests a difference as to greater practicability and probability of success on one as compared with the other ; the artery of the right side being longer than the left presents greater room for the application of a ligature at a sufficient distance, whether from the seat of the disease or from the origin of the vessel, while that of the left being more per pendicular in its course and nearer to the left side of the body ought to be more easily ex posed ; but it is to be recollected that this dis position is not uniformly present.
Before undertaking an operation upon any of the iliac arteries it will be advantageous to determine, so far as possible, the relation of the vessel, which is to be the subject of it, to the superficial points of the abdominal wall. This must be understood to be intended only as an approximation, but by attention to the follow ing circumstances it will prove sufficiently close to serve the desired purpose. The mean point, at which the aorta divides and the pri mitive iliac commences, is half an inch below the umbilicus at its left side, and that at which the external iliac terminates is midway between the symphysis pubis and the superior anterior spinous process of the ilium : of course a line connecting these points will define the general course of the primitive and external iliac arte ries. The length of the primitive iliac being from two to three inches, the extent of its course may be determined by the subdivision of this line. The point of demarcation be tween the primitive and external iliacs, and which will serve to mark the origin of the in ternal and external, as well as the termination of the primitive, may be further determined by a line extending from the crest of the ilium about one inch and a half behind its anterior superior spinous process to a similar point on the other side; such a line will traverse the sacro-vertebral articulation posterifir to the di vision of the primitive iliac, and by its decus sation with that before mentioned will mark more particularly the point of division of the vessel,* which will also correspond nearly to the centre of a line drawn from the anterior superior spinous process of the ilium to the umbilicus.t
The practicability and success of these ope rations have been so long established that they do not now require to be insisted upon.
When the external iliac has been tied below the origin of the epigastric and circumflex ilii branches, the circulation of the limb is main tained through the communications of the branches of the internal iliac with those of the femoral, of which the principal have been ascertained by Sir A. Coopers to be the gluteal with the external circumflex, the obturator with the internal circumflex, and the ischiatie with the profunda, and through those of the circumflex iliac with the same. (See FEMORAL ARTERY.) When the ligature has been applied above the origin of these branches, the circulation is esta blished also through their communications with the internal iliac, the internal mammary, the inferior intercostal and lumbar arteries.
The ligature of the internal iliac artery can cause little interruption of the supply of blood to the parts to which it is distributed ; its com munications are so numerous and free, exter nally and inferiorly with the external iliac and femoral arteries; inward with that of the other side, and upward with the aorta through the middle sacral and hemorrhoidal arteries, that the obstruction of the main trunk can affect it but little.
When the primitive iliac has been tied the circulation must be restored by means of the communication which exists between the arte ries of the upper and lower extremities through the internal mammary and epigastric arteries, of that between the aorta and the iliac arteries, through the intercostal, lumbar, middle sacral, hemorrhoidal, and the branches of the latter, and of that between the iliac arteries of both sides.