418 ABDOMINAL AOETA ILIAC AllTERIES. 



These anastomoses constitute a well-marked vascular plexus, situated in the sub- 

 peritoneal tissue, whence Turner proposes to call them the subperitoneal arterial 

 plexus. It occupies the lumbar region from the diaphragm downwards into the iliac 

 regions and pelvis, and establishes communication between the parietal vessels and 

 those of the viscera, chiefly, though not exclusively, through branches of the arteries 

 of those viscera which are situated behind the peritoneum. It belongs to the renal 

 and suprarenal arteries, those of the pancreas and duodenum, the caecum, and the 

 ascending and descending parts of the colon. It extends also to the vessels of the 

 rectum, and to the spermatic arteries in their descent through the abdomen, and into 

 the inguinal canal and scrotum. 



In these situations it was found that the injected material (coloured gelatine) 

 when thrown into the vessels of the viscus, so as to fill them completely, extended 

 through the subperitoneal plexus in various ways, so as to reach one or other set of 

 parietal vessels, such as the lumbar, ilio-lumbar, circumflex iliac, lower intercostal 

 and epigastric arteries ; and in the pelvis, the middle and lateral sacral arteries ; and 

 in the scrotum, the superficial pudic and perineal arteries. 



The more direct inosculations of the hDcmorrhoidal arteries on the rectum with the 

 inferior hasmorrhoidal branches of the pubic artery are well known, and the importance 

 of these and other similar anastomoses, as well as the more extensive and minute 

 anastomosing plexus investigated by Turner, is obvious, with reference not merely to 

 the nutrition of the subperitoneal tissue, but also to the debated question of the 

 influence exerted by local superficial blood-letting on the state of the vessels of the 

 deeper viscera. 



III. MIDDLE SACRAL ARTERY. 



The middle sacral artery, the last of the branches of the abdominal aorta, 

 is a small vessel of about the size of a crowquill, which arises from the 

 extremity of the aorta just at the bifurcation. From this point the artery 

 proceeds downwards upon the last lumbar vertebra and over the middle of 

 the sacrum, as far as the coccyx, where it forms small arches of anastomosis 

 with the lateral sacral arteries. 



BRANCHES. From its anterior surface some small branches come forward Avithin 

 the fold of the meso-rectum, and ramify upon the posterior surface of the intestine ; 

 and on each side others spread out upon the sacrum, and anastomose Avith the lateral 

 sacral arteries, occasionally sending small offsets into the anterior sacral foramina. 



The middle sacral artery sometimes deviates a little to the side, and proceeds, not 

 from the bifurcation of the aorta, but from one of the common iliac arteries, usually 

 from that of the left side. This artery represents the caudal prolongation of the aorta 

 of animals. 



COMMON ILIAC ARTERIES. 



The common iliac arteries, commencing at the bifurcation of the aorta, 

 pass downwards and outwards, diverging from each other, and divide opposite 

 the lumbo-sacral articulation into the internal and external iliac arteries. 



The common iliac arteries measure usually about two inches in length. 

 Both are covered by the peritoneum and the intestines, and are crossed by 

 thj ureters near their point of division, as well as by the branches of the 

 sympathetic nerve which are directed towards the hypogastric plexus. 

 They rest on the bodies of the vertebras, and come into contact with the 

 psoas muscles. 



The common iliac artery of the right side is separated from the front of 

 the last lumbar vertebra, the two common iliac veins being interposed. The 

 artery of the left side is crossed by the branches of the inferior mesenteric 

 vessels. 



Relation to Veins. The lefc iliac vein, supported on the last lumbar 



