THE SUPRARENAL AND RENAL ARTERIES. 465 



(c) The superior hwmorrhoidal artery, the continuation of the inferior mesen- 

 teric, passes downwards, over the left common iliac vessels, into the pelvis behind 

 the rectum, lying at first in the mesorectum, and then divides into two branches 

 which extend one on each side of the intestine towards the lower end. About five 

 inches from the anus these subdivide each into three or four branches which pierce 

 the muscular coat some two inches lower down. In the wall of the intestine, these 

 arteries, placed at regular distances from each other, descend between the mucous 

 and muscular coats to the end of the gut, where they communicate in loops opposite 

 the internal sphincter, and anastomose with the middle and inferior hsemorrhoidal 

 arteries. 



Varieties. Absence of the inferior messnteric arbeiy has been met with, its branches 

 being given off by the superior mesenteric. It has also been found giving origin to the 

 middle colic artery, and accessory branches to the liver and kidneys. 



A mithJli' mt'wntt'rir artery, arising from the common iliac and supplying vessels to the 

 transverse and descending colon, has been seen by Hyrtl. 



Anastomoses on the alimentary canal. The arteries distributed to the alimentary 

 canal communicate freely with each other over the whole length of that tube. The arteries 

 of the great intestine, derived from the two mesenteric trunk?, form a series of vascular 

 arches along the colon and rectum, at the lower end of which they anastomose with the 

 middle and inferior haemorrhoidal arteries, given off from the internal iliac and pudic 

 arteries. The branches from the left side of the superior mesenteric form another series of 

 arches along the small intestine, which is connected with the former by the ileo-colic artery. 

 Farther, the inferior pancreatico-duodenal branch of the superior mesenteric joins upon the 

 duodenum with the superior pancreatico-duodenal artery. The latter is derived from the 

 same source as the pyloric artery ; and so likewise, through the coronary artery of the stomach 

 and its ascending branches, a similar connection is formed with the oesophageal arteries, even 

 up to the pharynx. 



The middle suprarenal or capsular arteries (vi) are two very small vessels 

 which arise from the aorta on a level with the superior mesenteric artery, and pass 

 obliquely outwards upon the crura of the diaphragm to reach the suprarenal cap- 

 sules, to which bodies they are distributed, anastomosing at the same time with the 

 upper and lower suprarenal branches derived respectively from the phrenic and the 

 renal arteries. In the foetus these arteries are relatively of large size. 



Varieties. This artery is often very small, its place being supplied by the superior and 

 inferior suprarenals. The middle suprarenal sometimes gives off the spermatic artery, more 

 frequently on the left than on the right side. 



The renal or emulgeut arteries (ii), of large size in proportion to the bulk 

 of the organs which they supply, arise from the sides of the aorta, about half an 

 inch below the superior mesenteric artery, that of the right side being generally a 

 little lower down than that of the left. Each is directed outwards so as to form 

 nearly a right angle with the aorta. In consequence of the position of the aorta 

 upon the spine, the right renal artery has to run a somewhat longer course than the 

 left, and it also crosses behind the inferior vena cava. Both right and left arteries 

 are overlapped by the accompanying renal veins. Before reaching the hilum of the 

 kidney, each artery divides into four or five branches, the greater number of which 

 usually lie between the vein in front and the pelvis of the ureter behind. These 

 branches, after having passed deeply into the sinus of the kidney, subdivide and are 

 distributed in the gland, in the manner described in the account of the structure of 

 that organ. 



Each renal artery, before entering the hilum of the kidney, furnishes one or two 

 small branches to the suprarenal body (inferior suprarenal arteries), to the ureter, to 

 the lumbar lymphatic glands, and several twigs which ramify in the connective 

 tissue and fat around the kidney. 



Varieties. Irregularities of the renal arteries are met with in about 25 per cent. The 

 commonest is the presence of an additional vessel (in about 20 per cent.), an accessory artery 



