PAKIETAL BKANCHES OF THE ABDOMINAL AOETA. 933 



artery, and (ii.) a descending branch to the upper part of the descending colon. The lower 

 branch passes to the left, behind the peritoneum, and divides into upper and lower divisions ; 

 the upper anastomoses with the descending division of the upper branch and supplies 

 the lower part of the descending colon. The lower division supplies the iliac colon, and it 

 anastomoses with the branches of the upper division and with the branches of. the sigmoid 

 arteries. Both branches of the left colic artery lie immediately behind the peritoneum, 

 and each branch crosses anterior to the ureter and the internal spermatic vessels. 



(6) The sigmoid branches, usually two in number, arise from the convexity of the 

 inferior mesenteric, and pass downwards and to the left to the lower part of the iliac 

 colon and to the pelvic colon. They lie posterior to the peritoneum, and anterior to the 

 psoas major, the ureter, and the upper part of the iliacus. They terminate by dividing into 

 branches which anastomose with the terminal twigs of the lower branch of left colic 

 above and with branches of the superior hsemorrhoidal below, forming a series of arches 

 from which branches are distributed to the lower part of the iliac colon and the pelvic colon. 



(c) The superior haemorrhoidal artery 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 minor 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 hsemorrhoidal 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 one another, with offsets from the middle 

 haemorrhoidal branches of the internal iliac arteries, the inferior hsemorrhoidal branches 

 of the internal pudic arteries, and with branches from the middle sacral artery. 



The superior haemorrhoidal artery supplies the mucous membrane of the pelvic colon 

 and the rectum and the muscular coats of the pelvic colon. 



PARIETAL BRANCHES OF THE ABDOMINAL AORTA. 



1. Arterise Phrenicae Inferiores. The inferior phrenic arteries (Fig. 773), 

 right and left, are of . small size ; they arise, either separately or ' by a common 

 i trunk, from the aorta, immediately below the diaphragm, to which they are dis- 

 tributed. Diverging from its fellow, each artery runs upwards and laterally, on 

 the corresponding crus of the diaphragm that on the right side passing posterior 

 to the inferior vena cava, that on the left side posterior to the oesophagus and just 

 1 before reaching the central tendon of the diaphragm each divides into medial and 

 lateral terminal branches. The medial branch runs forwards and anastomoses 

 with its fellow of the opposite side, forming an arch, convex forwards, along the 

 anterior border of the central tendon of the diaphragm. Offsets from this arch 

 , anastomose with the pericardiaco-phrenic, musculo-phrenic, and internal mammary 

 arteries. The lateral branch passes laterally towards the lower ribs, and anastomoses 

 with the musculo-phrenic and lower intercostal arteries. 



In addition to supplying the diaphragm each inferior phrenic artery gives a 

 superior suprarenal branch, to the suprarenal gland of its own side, and, occasionally, 

 small hepatic branches which pass through the coronary ligament to the liver. 

 Further, the left artery gives oesophageal branches which anastomose with 

 1 oesophageal branches of the aorta and of the left gastric artery, whilst from the 

 artery of the right side minute branches pass to the inferior vena cava. 



!. Arteriae Lumbales. The lumbar arteries correspond to the intercostal 

 branches of the thoracic aorta. They are in series with the intercostal arteries ; 

 their distribution is very similar; and, like the intercostals, they arise, either 

 separately or by common trunks, from the posterior aspect of the aorta. 



There are usually four pairs of lumbar arteries, but occasionally a fifth pair 

 1 arises from or in common with the middle sacral artery. 



From their origins the lumbar arteries pass laterally and posteriorly, across the 

 ront and sides of the bodies of the upper four lumbar vertebrae, to the intervals 

 bween the adjacent transverse processes, beyond which they are continued into 

 the lateral part of the abdominal wall. 



Each artery lies on the body of the corresponding lumbar vertebra. In its back- 



r course, and while still in relation with the vertebral body, it is crossed 

 60 I 



