External to both, but on a plane posterior to them, are the pso muscles, the left artery how ever being nearer to the muscle than the right, between which and the psoas the right primitive vein and the cava intervene, being at the same time posterior to it.
Internal to both at their origin is the middle sacral artery ; on the left side the left primitive vein lies along the inside of the artery, but on a plane behind it.
Anteriorly the arteries are crossed at their termination by the corresponding that duct being interposed between the peritoneum and the vessel, but more adherent to the former. The relation of the ureter to the iliac arteries is not uniform, either on opposite sides or in different subjects; the bifurcation of the pri mitive iliac may be assumed as the mean point of reference for its transit, the duct descending into the pelvis between the external and internal iliacs, and before the internal ; hut its precise relation will depend upon the height at which the bifurcation takes place and the side of the body to which it belongs, and hence it very frequently, if not usually, crosses the external iliac upon the right and the termination of the internal on the left.
The artery and vein, the relations of which differ remarkably upon the two sides, the vein being external upon the right and internal upon the left, and upon both posterior, are enclosed within a condensed cellular investment, pro longed upward upon the aorta and downward upon the secondary iliacs ; upon the primitive vessels it is so thin that it may at times seem absent; but, as it descends, it increases in thickness, and acquires upon the external iliacs considerable strength.
The primitive iliac arteries ordinarily give only minute branches to the adjoining parts, viz. the ureter, the peritoneum, the vein, lym phatic glands and cellular structure; but occa sionally they have been found to give off the ilio-lumbar artery, and more rarely a renal or spermatic artery..
Although,according to the view usually taken, the primitive iliac terminates by dividing into internal and external, yet in many instances it will be found that the primitive and external iliacs appear as one vessel giving off the internal From its posterior side, and nearly at right angles, while in the foetus the reverse seems the case, the primitive and internal being continuous and rather giving off the external.