MIDDLE SACEAL ARTEEY. 437 



their iiatm-e elucidated by W. Turner in a series of experimental injections, made 

 with a view to their detection. (" Brit, and For. Med. Chii-ug. Review " July 



18g:j.) 



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

 subperitoneal tissue, which Turner calls the ffuJqnrltonrdl arterial jjlcriiK. It 

 occupies the lumbar region from the diaphragm downwards into the iliac refions 

 and pelvis, and establishes communication between tlie parietal vessels and those 

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

 of those viscera which are s-ituated behind the peritoneiun. It belongs to the 

 renal and suprarenal arteries, those of the pancreas and duodenum, the cajcum. 

 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 thi-o-mi 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, cii-cimiflex 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 hajmorrhoidal arteiies on the rectum with 

 the inferior hasmon-hoidal 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. 



Middle sacral artery, — The middle sacral artery, the last of the 

 branches of the abdominal aorta, is a small vessel about the size of a 

 crowquill, which arises ft'om the extremity of tlie 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 foiTvard 

 within 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 anasto- 

 mose with the lateral sacral arteries, occasionally sending small offsets into the 

 anterior sacral foramina. 



Varieties. — The middle sacral artery sometimes deviates a little to the side. 

 It may proceed, 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 otlier, 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 the ureters near their point of division, as well as by the 

 branches of the sympathetic nerve which are directed towards the hypo- 

 gastric plexus. They rest on the bodies of the vertebrae, and come into 

 contact with the psoas muscle. 



