This artery sometimes arises in common with the cceliac axis. It has been known to give off an hepatic artery, and in another case it gave off the gastro-epiploica dextra.

The superior mesenteric artery may be absent; or its branches may not anastomose with those of the inferior mesenteric artery; or it may be double. In a case of high division of the aorta, the superior mesenteric has come from the internal iliac.

Varieties Of The Inferior Mesenteric Artery

This artery may be wanting. In a very remarkable case where the right kidney and its artery were absent, the common iliac arteries were united by a transverse branch, and from the left common iliac came off the inferior mesenteric*

Varieties Of The Phrenic Arteries

Both phrenics have been found arising by a common origin from the right emulgent; or they may arise by a common origin from the aorta; or one or both may come from the cceliac axis. Sometimes they arise from the first lumbar, but rarely from the gastric or renal.

Varieties Of The Capsular Arteries

These arteries are very small in the adult, but as large as the renal in the foetus: there are often three or four of them. The supra- * renal capsules have arteries from three different sources, viz.: from the inferior phrenic, from the aorta, and from the renal arteries.

Varieties Of The Renal Arteries

These arteries are liable to many varieties, affecting their number, origin, direction, and branches given off from them.

Number

In some cases there are two on one or both sides: when this occurs on the right side, one branch usually goes behind and the other in front of the inferior cava. Occasionally there is a distinct artery sent to one of the extremities of the kidneys; this may be either a branch of the renal, or it may arise separately from the aorta, internal iliac, or middle sacral, or from the common iliac. In one very extraordinary case the kidney was placed transversely in the pelvis and supplied by the middle sacral artery. Portal saw the right and left arteries arise by a common origin from the aorta. The right renal artery and kidney may be absent.

* Petsch, Syl. Observ. Anat. Select., § 76. Archives Generales, Fev. 1835.

Origin

The renal artery may arise lower down than usual from the aorta; or it may come from the common or internal iliac : this is more likely to occur when the kidney is found in the iliac fossa, as sometimes happens. Cruveilhier has seen an accessary branch, from the bifurcation of the aorta, go to the kidney in this situation. Meckel has seen the two renal arteries arise by a common trunk from the front of the aorta.

Direction

The renal arteries usually form somewhat less than a right angle with the continued trunk; but their direction must obviously vary according as they rise high or low. In some cases in which there were two renal arteries on one side, they were found twisted on each other like the umbilical arteries.

Branches From The Renal Arteries

The spermatic arteries on one or both sides may arise from these arteries.