| . ABNORMALITIES OF ARTERIES. ' 899 
it may be considerably above, or more rarely it may spring directly from the bifurcation. Not 
infrequently if arises from the last lumbar artery or from a stem common to the two last 
lumbar arteries, and occasionally it arises from a common or internal ilae artery. Some- 
times it apparently gives off the last pair of lumbar arteries, and very occasionally an accessory, 
renal, or a hemorrhoid: al branch arises from it. The vessel is not always present, it may be 
double, entirely or in part, and it may bifurcate at its termination. 
The renal arteries frequently deviate from the normal arrangement. The arteries of 
opposite sides may spring from a common stem, or there may be two or more renal arteries on 
one or both sides. The accessory arteries are more common on the left than on the right side, 
and an accessory artery rising above the ordinary vessel is more common than one rising 
below it. 
Accessory renal arteries may be derived not only from the aorta, but also from the common 
or internal iliac arteries; they have also been described as arising from the inferior phrenic, 
spermatic, lumbar, ot middle sacral arteries, and even from the external iliac artery. As the 
kidney is developed in the region of the first sacral vertebra, and afterwards ascends to its perma- 
nent position, it is not surprising that it occasionally receives arteries from the main stem of 
more than one of the segments of the body through which it has passed, and it is usually found 
that the lower the position of the kidney in the abdomen the more hkely it is to receive its 
arteries from the lower part of the aorta or from the common iliac arteries. |The accessory renal 
arteries which spring from the inferior phrenic, the spermatic, and lumbar arteries can only be 
the result of the persistence and enlargement of anastomosing channels between the renal and 
either another intermediate visceral, or a somatic artery. 
The spermatic or ovarian arteries may be double on one or both sides ; the arteries of oppo- 
site sides may spring from a common trunk, or they may rise from the renal or suprarenal 
arteries. The right artery may pass behind instead of in front of the inferior vena cava. The 
spermatic and ovarian arteries arise from the upper lumbar portion of the aorta, because the 
testicles and ovaries are developed in and obtain their arterial supply in that region, and the 
vessels are elongated as the testicles and ovaries descend to their permanent positions. The 
occurrence of two spermatic arteries on one side is probably an indication that the testicle was 
developed in at least two segments of the body, and the origin of a spermatic artery from a renal 
or suprarenal artery is due to the obliteration of the root of the original vessel and the enlarge- 
ment of an anastomosis between the intermediate visceral arteries of adjacent segments. 
The coeliac axis may be absent, its branches arising separately from the aorta or from some 
other source. Sometimes it gives off only two branches, usually the coronary and splenic, and 
oceasionally it gives four branches, the additional branch being either a second coronary artery 
or a separate gastro-duodenal artery. 
The hepatic artery may spring directly from the aorta or from the superior mesenteric 
artery, and the left hepatic artery occasionally arises from the coronary artery. Accessory hepatic 
arteries are not uncommon, and they originate either from the coronary, superior mesenteric, renal, 
or inferior mesenteric artery. 
The coronary artery is occasionally double; it may spring directly from the aorta, and it 
may give off the left hepatic or an accessory hepatic artery. 
"The splenic artery may arise from the middle colic, from the left hepatic, or from the 
inferior mesenteric artery. 
The superior mesenteric artery may be double, and it may supply the whole of the 
alimentary canal from the second part of the duodenum to the end of the rectum, the inferior 
mesenteric artery being absent. In addition to its ordinary branches it may give off a hepatic, 
a splenic, a pancreatic, a gastric, a gastro-epiploic or a gastro-duodenal branch. Very rarely 
it gives off an omphalo-mesenteric branch, which passes to the region of the umbilicus and 
becomes connected with capillary vessels in the faleiform hgament of ‘the liver. 
The inferior mesenteric artery may give hepatic, renal, or middle cole branches ; occasion- 
ally it is absent, being replaced by branches of the superior mesenteric, and sometimes, as in 
ruminants and some “rode mts, its left cole branch does not anastomose with the middle 
colic artery. 
All these variations of the unpaired visceral branches of the abdominal aorta are merely due 
to modifications of the usual processes by which these vessels are developed. 
The origin of the branches which usually rise from the cceliae axis, from the trunk of the 
aorta is the result of the retention of a greater number of the splanchnic segmental arteries 
than usual. A double superior mesenteric ‘artery results from the persistence of both the right 
and left splanchnic vessels from which the superior mesenteric artery is formed, these remaining 
separate instead of fusing together. All the other variations are the results of the obliteration 
of the usual channels, combined with the enlargement of anastomoses which exist both 
between the splanchnic arteries of adjacent segments and the splanchnic and intermediate 
visceral arteries. 
: THE ARTERIES OF THE HEAD AND NECK. 
Innominate Artery.—From what has already been said with reference to the branches 
of the arch of the aorta, it will be seen that the innominate artery may be absent. On the other 
hand there may be two innominate arteries, a right and a left, each ending in corresponding 
common carotid and subclavian trunks, and the two vessels may ‘themselv es arise by a common 
stem. 
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