PRIMITIVE ILIAC ARTERIES (common artcrie iliac& primitive, S. communes, s. pclvi cruraks; Fr. Art?rcsilioqucs primitives; Germ. Ccreeinsehaftliehe 110-pulsadcrn,) are two, one on each side : they are vessels of great size, from three-eighths to four-eighths of an inch in diameter, but short, their length varying from one and a half to two and a half or three-quarters of an inch, the arteries being longer or shorter, according to the height at which the aorta divides. They arise from the termination of the aorta, their ongin corresponding, as a mean point, to the in terval between the bodies of the fourth and fifth lumbar vertebra, and somewhat to the left of the middle line of the vertebral column ; the exact height of their origin, however, varies considerably, ranging in ordi nary between the bodies of the third and fifth vertebra ; but they have been found to arise very near to the diaphragm' From their origin they descend, and at the same time in cline outward and backward, forming with each other an acute angle, but more so in the male than in the female subject, because of the greater width of the pelvis in the latter, until they reach a point ranging between the body of the fifth lumbar vertebra and the sacro-diac artieulation,t where they terminate by dividing into the internal and external iliacs. The point of reference usually assigned for this division is the sacro-iliac articulation ; but this appears not to be strictly correct, the exact point varying as well on the opposite sides of the same as in different subjects; for the most part the division takes place between the two points, which have been mentioned ; at times nearer to one, at times to the other, and according to l'elpeau, it usually occurs nearer to the spine upon the right than upon the left side; hence, according to the same authority, the right external iliac artery is longer than the left, and were it pos sible to ascertain these diversities of origin during life, advantage would result therefrom, inasmuch as the prospect of success in high ligature of the external iliac must be influenced by the height of its origin, and the difficulty of reaching the primitive or the internal iliacs must be increased in the same proportion. These views appear well-founded ; the division of the primitive iliac rarely takes place so far outward as the saero-iliac articulation, and for the most part it is nearer to the body of the vertebra, or higher upon the right than the left side, and therefore the external iliac of that side is usually the longer, but this disposition is not constant; the division of the right primitive artery is not always higher than that of the left, nor conse quently the right external longer, and therefore while probability is in favour of the conclusion which the facts stated indicate, it cannot be absolutely relied upon.
The primitive iliac arteries are of the same size, and nearly the same length ; the right, however, is considered for the most part some what the longer, because of the situation of the aorta upon the left side of the spine ; Velpcau, however, seems to question the existence of any difference in the length of the two vessels, inas much as the right divides generally nearer to the spine than the left, the inclination of their origin to the left being thus compensated, but to what ever extent this view may hold good, it is by no means strictly correct ; in filet the length of the arteries, whether comparative or absolute, is far from regular; nor is the preponderance, when present, always upon the same side; the opinion generally entertained is probably correct, the right artery being in the majority of instances somewhat longer than the left; but the writer has found the left the longer of the two, and the same disposition has been observed by J. F. Meckel; this is,however, an unusual disposition.
The relations of the arteries are simple. Durkig their descent they are situate in front of the bodies of the lumbar vertebra:, with the intervening fibro-cartilages, of one, two, or more of these bones, according to the height at which the arteries arise, and also of the lateral part of the base of the sacrum ; they are both covered upon three sides by the peritoneum, viz. in front and laterally, the membrane descending upon them from the root of the mesentery; the mesentery itself also and the small intestines are placed before them, and the latter overlap them upon either side. Farther, they are in front of the superior branches of the middle sacral artery and of the sympathetic nerve. That of the right side at its outset is placed before the left primitive iliac vein, which it crosses at its junction with the eava, and par tially before the commencement of the cava itself; during its course it is in front of the right primitive vein, at first only partially, but, as it proceeds, covering it to a greater extent, until at its termination it is directly before it.