556 



THE BLOOD-VASCULAR SYSTEM. 



and run downward, as straight vessels, placed at regular intervals from each other 

 in the wall of the gut between its muscular and mucous coat, to the level of the 

 internal sphincter ; here they form a series of loops around the lower end of the 

 rectum, and communicate with the middle hgemorrhoidal arteries, branches of the 

 internal iliac, with the inferior hsemorrhoidal branches of the internal pudic. 



Middle haemorrhoidal 

 Inferior hsemorrhmdalt 



FIG. 311. The inferior mesenteric and its branches. 



The Suprarenal Arteries (Fig. 307). 



The suprarenal arteries are two small vessels which arise, one on each side of 

 the aorta, opposite the superior mesenteric artery. They pass obliquely upward 

 and outward, over the crura of the Diaphragm, to the under surface of the supra- 

 renal capsules, to which they are distributed, anastomosing with capsular branches 

 from the phrenic and renal arteries. In the adult these arteries are of small size ; 

 in the foetus they are as large as the renal arteries. 



The Renal Arteries (Fig. 307> 



The renal arteries are two large trunks which arise from the sides of the aorta 

 immediately below the superior mesenteric artery. Each is directed outward 

 across the crus of the Diaphragm, so as to form nearly a right angle with the 

 aorta. The right is longer than the left, on account of the position of the aorta ; 

 it passes behind the inferior vena cava. The left is somewhat higher than the 



