THE COMMON ILIAC AETEKIES. 935 



The abdominal aorta is almost median in position, consequently the right 

 lumbar arteries are scarcely longer than the left. On the right side the arteries 

 pass behind the inferior vena cava, the upper two arteries being separated from 

 that vessel by the right crus of the diaphragm. The upper two right arteries also 

 pass posterior to the cisterna chyli and the lower end of the azygos vein. 



Branches. Dorsal. Each lumbar artery gives off, opposite the interval between 

 the vertebral transverse processes, a dorsal branch of considerable size. It is analogous 

 with and is distributed like the posterior branch of an aortic intercostal artery (p. 925). 

 Muscular branches are given off, both from the main trunk and its dorsal branch, to 

 the adjacent muscles. 



3. Arteria Sacralis Media. The middle sacral artery (Fig. 773) is a single 

 median vessel. It is commonly regarded as a caudal aorta and as the direct 

 continuation of the abdominal aorta. It is, however, of small size, and almost 

 invariably arises from the back of the aorta, about 12 mm. (half an inch) above 

 its bifurcation. It descends, anterior to the lower two lumbar vertebrse and 

 to the sacrum and coccyx, and ends, opposite the tip of the coccyx, by 

 anastomosing with the lateral sacral arteries to form a loop from which branches 

 pass to the coccygeal glomus. Opposite the fifth lumbar vertebra it is crossed, 

 anteriorly, by the left common iliac vein, below which it is covered by peritoneum 

 and coils of small intestine as far -as the third segment of the sacrum, and in the 

 rest of its extent it is posterior to the rectum. It is accompanied below by 

 venae comites, which, however, unite, above, to form a single middle sacral vein. 



As it lies anterior to the last lumbar vertebra it gives off on each side a 

 lumbar branch, the arteria lumbalis ima, which is distributed like an ordinary 

 lumbar artery, and as it descends in front of the sacrum it distributes small 

 parietal branches laterally which anastomose with the lateral sacral arteries. The 

 parietal branches usually give off small spinal offsets which enter the anterior sacral 

 foramina. Small and irregular visceral branches pass to the rectum and anastomose 

 with the superior and middle hgemorrhoidal arteries. 





ARTERIA ILIAC.E COMMUNES. 



, The common iliac arteries (Figs. 773 and 774) are the terminal branches 

 of the abdominal aorta. They commence opposite the middle of the body of the 

 fourth lumbar vertebra a little to the left of the median plane. Each artery passes 

 downwards and laterally, across the bodies of the fourth and fifth lumbar vertebrae 

 and the intervening intervertebral fibro-cartilage, and it terminates, at the level 

 of the lumbo-sacral articulation and anterior to the corresponding sacro-iliac joint, 

 by dividing into external iliac and hypogastric (O.T. internal iliac) branches. 



The direction of each common iliac is indicated by a line drawn from the 

 bifurcation of the aorta to a point midway between the symphysis pubis and the 

 anterior superior spine of the ilium. 



The right artery is a little longer than the left ; the former being about 50 mm. 

 two inches) and the latter 43 mm. (one and three-quarter inches) in length. 



Relations. Anterior. Both arteries are covered anteriorly by peritoneum, and are 

 separated by it from coils of the small intestine. Communicating branches between the 

 aortic and hypogastric plexuses of the sympathetic pass in front of the arteries, each of which 

 is often crossed, anteriorly, near its termination by the corresponding ureter. 

 The left artery is crossed, in addition, by the superior hsemorrhoidal vessels. 

 Posterior. Behind the artery, of each side, are the bodies of the fourth and fifth 

 lumbar vertebra, and the intervening intervertebral fibro-cartilage, the sympathetic trunk, 

 the psoas major muscle. These relationships, however, are much closer on the left side 

 lan on the right. The right common iliac, except at its lower end, where it is in contact 

 ith the psoas major, is separated from the structures named by the terminations of the 

 right and left common iliac veins and the commencement of the inferior vena cava. The 

 common iliac, which is not so separated, lies on the medial border of the psoas major. 

 x>mewhat deeply placed, in the areolar tissue between the psoas major and the lumbar 





