BRANCHES OF THE ABDOMINAL AORTA 571 



III. The renal arteries (Aa. renalos), right and left, are relatively large vessels 

 which arise from the aorta near the anterior mesenteric. The right artery is the 

 longer of the two. It crosses over the dorsal surface of the vena cava to the right 

 and somewhat forward. At the hilus it divides into several (five to eight) branches; 

 some of these enter the gland at the hilus, while others pass to the ventral surface 

 and enter there. The left artery is short and usually arises a little further back; 

 it i^asses directly outward to the kitlney and is then disposed like the right one. 

 Small collateral branches are supplied to the ureters and the adrenals. Tlie latter 

 also receive small vessels directly from the aorta. The distribution within the 

 kidney has been described. 



Variations in the renal arteries are frequent. Two or more arteries may occur on one or 

 both sides. Accessory arteries are more common on the left side and usually enter the posterior 

 pole of the gland. They may arise from the aorta, the external iliac, or the circumflex iliac artery. 



IV. The posterior or small mesenteric artery (A. mesenterica caudalis) is an 

 unpaired vessel which arises from the \-entral face of the aorta at the fourth lumbar 

 vertebra, i. c, about five or six inches (ca. 12 to 15 cm.) behind the origin of the 

 anterior mesenteric artery. It is much smaller than the latter and supplies the 

 greater part of the small colon and rectum. It descends in the colic mesentery 

 and divides into two branches. The anterior branch (A. colica sinistra) gives off 

 three or four arteries which divide and form anastomotic arches close to the bowel. 

 The first arch is formed by union with the middle colic branch of the anterior 

 mesenteric. The j^osterior branch or anterior ha^morrhoidal artery (A. hsemor- 

 rhoidalis cranialis) passes backward in the upper part of the mesentery and the 

 mesorectum and terminates near the anus by anastomosing Avith the internal 

 pudic artery. Three or four of its anterior collateral branches form arches. 



V. The spermatic arteries (Aa. spermaticae internee), right and left, are long 

 slender arteries which arise from the aorta near the posterior mesenteric and supply 

 the testicle and epididymis. Each passes backward in a narrow fold of peritoneum 

 (Plica vasculosa) to the internal inguinal ring and descends through the inguinal 

 canal to the scrotum. In the canal and scrotum it pursues a very fiexuous course 

 in the anterior border of the spermatic cord, surrounded by the pampiniform plexus 

 of veins, and associated closely with the spermatic nerves and lymphatics and 

 unstriped muscle-fibers. It passes between the epididymis and testicle, runs in 

 fiexuous fashion along the attached border of the latter, turns around the posterior 

 pole, and runs forward on the free border to the anterior pole. The largest branches 

 arise from its ventral part, pass tortuously up either side of the gland embedded 

 in the tunica albuginea, and give off fine branches to the gland substance. Small 

 collateral branches are detached to the ureter and the spermatic cord. 



The utero-ovarian arteries in the female correspond to the preceding 

 vessels, but are much shorter. Each is placed in the anterior part of the broad 

 ligament of the uterus and divides into ovarian and uterine branches. The ovarian 

 branch (A. ovarica) pursues a fiexuous course to the ovary, which it supplies. The 

 uterine branch (A. uterina cranialis) passes to the concave border of the cornu of 

 the uterus, which it supplies, anastomosing with the uterine artery. 



VI. The lumbar arteries (Aa. lumbales) are in series with the intercostal 

 arteries and have a similar origin and distribution. There are usually six pairs of 

 lumbar arteries, of which five arise from the aorta and the sixth from the internal 

 iliac or the lateral sacral at the junction of the last lumbar vertebra and the sacrum. 

 Each passes across the body of a lumbar vertebra to the intertransverse space, 

 gives branches to the sublumbar muscles, and divides into dorsal and ventral 

 branches. The dorsal branch (Ramus dorsalis), the larger of the two, passes 

 upward to ramify in the extensor muscles of the spine and the skin of the loins; 

 it gives off a spinal branch (Ramus spinalis) which comports itself like the corre- 

 sponding branch of an aortic intercostal artery. The ventral branch (Ramus 



