THE INTERNAL ILIAC ARTERY. 803 
from the front and towards the left side of the aorta an inch and a half above the 
bifurcation ; it passes downwards and slightly outwards, lying behind the periton- 
eum and on the front of the left psoas muscle, to the upper and outer border of 
the left common iliac artery, where it becomes the superior hemorrhoidal. 
Branches.—(«) The left colic artery (a. colica sinistra) arises from the left side of 
the inferior mesenteric near its origin. It runs upwards and to the left towards the splenic 
flexure of the colon, where it divides into ascending and descending branches. The 
ascending branch crosses in front of the lower end of the left kidney, passes between the 
layers of the transverse mesocolon, and, turning inwards, terminates by joining the left 
branch of the middle colic artery. The descending branch passes downwards behind the 
peritoneum to the inner side of the descending colon to unite with the superior sigmoid 
artery, and from the loops thus formed branches are distributed to the descending colon. 
In the whole of its course the left colic artery lies behind the peritoneum, and on the 
posterior abdominal wall ; it crosses in front of the left psoas, the left ureter, and the 
lower end of the left kidney. 
(6) The sigmoid branches (aa. sigmoidez), usually two in number, arise from the 
convexity of the inferior mesenteric, and pass downwards and outwards to the iliac 
colon. They lie behind the peritoneum, and in front of the psoas, the ureter, and the 
upper part of the iliacus. They terminate by dividing into branches which anastomose 
with the left colic above and with branches of the superior heemorrhoidal below, forming 
a series of arches from which branches are distributed to the lower part of the descending 
colon, the iliac colon, and the pelvic colon. 
(c) The superior hemorrhoidal artery (a. hemorrhoidalis superior) is the direct 
continuation of the inferior mesenteric. It enters the mesentery of the pelvic colon, 
crosses the front of the left common iliac artery, descends into the pelvis as far as the 
third piece of the sacrum, or in other words the junction between the pelvic colon and 
the rectum, and divides into two branches which pass downwards on the sides of the 
rectum. Half-way down the rectum each of the two terminal branches of the superior 
hemorrhoidal artery divides into two or more branches which pass through the muscular 
coats and terminate in the submucous tissue, where they divide into numerous small branches 
which pass vertically downwards, anastomosing with each other, with offsets from the middle 
hemorrhoidal branches of the internal iliac arteries, the inferior hemorrhoidal branches 
of the internal pudic arteries, and with branches from the middle sacral artery. 
The superior hemorrhoidal artery supplies the mucous membrance of the pelvic colon 
and the rectum and the muscular coats of the pelvic colon. 
THE INTERNAL ILIAC ARTERY. 
The internal iliac or hypogastric artery (a. hypogastrica, Figs. 566, 569, and 
572) in the foetus is the direct continuation of the common iliac trunk. It 
supplies numerous branches to the pelvis, runs upwards on the anterior abdominal 
wall to the umbilicus, and is prolonged as the umbilical artery to the placenta. 
One of its pelvic branches—the sciatic—is at first the main artery of the inferior 
extremity, but subsequently another branch is given off which becomes the chief 
arterial trunk of the lower imb. This branch is the external iliac artery; it soon 
equals and ultimately exceeds the internal iliac in size, and it is into these two 
vessels that the common iliac appears to bifureate. 
When the placental circulation ceases and the umbilical cord is severed, the 
part of the internal iliac trunk which extends from the pelvis to the umbilicus 
atrophies, and is afterwards represented almost entirely by a fibrous cord, known 
as the obliterated hypogastric artery. It is only at its proximal end that the 
atrophied part remains pervious, and here it forms the commencement of the 
superior vesical artery ; accordingly, the permanent internal iliac artery is a com- 
paratively short vessel. Owing to the arrangement of some of its branches it 
appears to end in an anterior and a posterior division, the former of which is to 
be regarded as the continuation of the vessel to the obliterated hypogastric, whilst 
the latter is simply a common stem of origin for some of the branches. 
With this explanation the internal iliae artery may be described in the 
usual manner. 
It arises from the common iliac opposite the lumbo-sacral articulation, and 
