THE COMMON ILIAC ARTERIES 603 



pelvis between the layers of the sigmoid meso-colon, and terminates on the rectum 

 in the superior hsemorrhoidal artery. It supplies the lower half of the large in- 

 testine. Its vein hes at first close to the left side, but soon passes upward on the 

 psoas, away from the artery, to end in the splenic vein (fig. 487). 



The branches of the inferior mesenteric are: — (1) The left colic; (2) the 

 sigmoid; and (3) the superior ha?morrhoidal. 



(1) The left colic artery [a. colica sinistra] runs transversely to the left, beneath the peri- 

 toneum, and divides into two branches, one of which, entering the transverse meso-colon, as- 

 cends upward and to the right, to anastomose with the middle colic. The other descends, and, 

 entering the sigmoid meso-colon anastomoses with the ascending branch of the sigmoid artery. 



The distribution of this artery, and of the next, to the colon is similar to that of the colic 

 branches of the superior mesenteric, and does not require a separate description. (See pp. 

 597, 598.) 



(2) The sigmoid artery [a. sigmoidea] runs downward and to the left over the psoas mus- 

 cle and, entering the sigmoid meso-colon, divides into two branches; the upper anastomosing 

 with the left cohc, the lower with the superior hsemorrhoidal. 



(3) The superior haemorrhoidal artery [a. hsemorrhoidahs superior] is the continued trunk of 

 the inferior mesenteric. It descends into the pelvis, behind the rectum, between the laj-ers of the 

 sigmoid meso-colon. On reaching the wall of the bowel it bifurcates, one branch proceeding on 

 either side of the gut, to within 10 or 12 cm. (4 or 5 in.) of the anus. Here each again divides, 

 and the branches, piercing the muscular coat, descend between that coat and the mucous mem- 

 brane, forming with each other, and with the middle hsemorrhoidal arteries — derived from the 

 hypogastric (internal iUac) — a series of small vessels, running longitudinally to the rectum, and 

 parallel to each other as far as the level of the internal sphincter, where, by their anastomosis, 

 they form a series of loops around the lower part of the rectum. 



C. The Terminal Branches of the Abdominal Aorta 

 THE MIDDLE SACRAL ARTERY 



The middle sacral artery [a. sacralis media], is, anatomically, the continuation 

 of the aorta. The cocc3^geal glomerulus [glomus coccygeum], in which it ter- 

 minates, is believed to contain the rudiments of the caudal aorta. The artery 

 extends from the bifurcation of the aorta to the tip of the coccyx. As it passes 

 downward into the pelvis, it runs behind the left common iliac vein, the hypo- 

 gastric plexus of the sympathetic nerve, and the peritoneum. It lies successively 

 upon the intervertebral disc between the fourth and fifth lumbar vertebrae, the 

 fifth lumbar vertebra, the intervertebral disc between that vertebra and the 

 sacrum, and lower down upon the anterior surface of the sacrum and coccyx. 



Branches. — The branches of the middle sacral artery are: — 



(1) The lowest lumbar artery [a. lumbalis ima], which, when present, usually comes off from 

 the middle sacral artery. Each vessel of this pair runs laterally beneath the common ihac artery 

 and vein; and, after giving off a dorsal branch, ramifies over the lateral part of the sacrum, and 

 ends in the iUacus muscle by anastomosing with the circumflex iliac artery. The dorsal branch 

 passes to the back between the last lumbar vertebra and the sacrum and ramifies in the gluteus 

 maximus, anastomosing with the lumbar arteries above, and the superior gluteal artery below. 



(2) Lateral sacral branches, are usually four in number. They are serially homologous with 

 the intercostal and lumbar arteries given off by the aorta. They run laterally, and anastomose 

 with the lateral sacral branches of the hypogastric (internal iliac) artery. They give off small 

 spinal branches, which pass through the sacral foramina, and supply the sacral canal and back 

 of the sacrum. 



(3) Rectal or haemorrhoidal branches pass forward beneath the peritoneum or in the sig- 

 moid meso-colon to the rectum, which they help to supply, and anastomose with the other 

 hsemorrhoidal or rectal arteries. 



THE COMMON ILIAC ARTERIES 



The common iliac arteries [aa. iliacse communes] arise opposite the left side 

 of the middle of the body of the fourth lumbar vertebra, at the bifurcation of the 

 abdominal aorta, and, diverging from each other in the male at about an angle 

 of 60°, and in the female at an angle of 68°, terminate opposite the lumbo-sacral 

 articulation by bifurcating into the external iliac, which is continued along the 

 brim of the pelvis to the lower limb, and into the hypogastric (internal iliac), 

 which passes through the superior aperture of the pelvis and descends into that 

 cavity (fig. 488). 



The relations differ slightly on the two sides, and may be considered separately. 



