Branches of the Abdominal Aorta

The collateral branches of the abdominal part of the aorta are distributed chiefly to the walls and contents of the abdominal cavity, but some branches are supplied to the spinal cord and its membranes, and others extend into the pelvis and to the scrotum. The visceral branches are the cœliac, anterior mesenteric, renal, posterior mesenteric, and the spermatic or utero-ovarian. The parietal branches are the lumbar arteries.

I. The cœliac artery or axis (A. cœliaca) is an unpaired vessel, usually half an inch or less (ca. 1 cm.) in length, which arises from the ventral aspect of the aorta at its emergence from the hiatus aorticus. It divides on the dorsal surface of the pancreas into three branches—the gastric, hepatic, and splenic.

1. The gastric artery (A. gastrica sinistra) passes downward and forward in the gastro-phrenic ligament, gives off œsophageal and pancreatic branches, and divides above and behind the cardia into anterior and posterior branches.

(a) The anterior branch (Ramus cranialis) crosses the lesser curvature just to the right of the cardia and ramifies on the parietal surface of the stomach. The branches pursue a flexuous course toward the greater curvature and anastomose with the short gastric arteries and the gastric branch of the hepatic artery.

(b) The posterior branch (Ramus caudalis) is distributed in a similar fashion on the visceral surface.

(c) The œsophageal branch (Ramus œsophageus) passes through the hiatus œsophageus into the thoracic cavity above the œsophagus and anastomoses with the œsophageal branch of the broncho-œsophageal artery.

The gastric artery often arises by a common trunk with the splenic. The two terminal branches may arise separately, or the anterior from the splenic and the posterior from the hepatic. The œsophageal branch often arises from the splenic or the posterior gastric.

2. The hepatic artery (A. hepatica) is larger than the gastric. It passes forward to the right and ventrally on the dorsal surface of the pancreas, covered by the gastro-pancreatic fold, crossing obliquely under the vena cava, and reaches the inner border of the portal vein. It divides into three or four branches which enter the portal fissure of the liver and ramify within the gland with the portal vein and the hepatic duct. It gives off the following collateral branches:

(a) Pancreatic branches (Aa. pancreaticæ) are given off as the artery crosses the pancreas, in which it is partly embedded.

(b) The pyloric artery (A. gastrica dextra) arises above the first curve of the duodenum. It descends to the pylorus, sending branches to the first part of the duodenum and the pylorus, and anastomoses with the gastric and right gastro-epiploic arteries. It may arise from the gastro-duodenal.

(c) The gastro-duodenal artery (A. gastroduodenalis) passes to the second curve of the duodenum and divides into the right gastro-epiploic and the pancreatico-duodenal. The right gastro-epiploic artery (A. gastroepiploica dextra) crosses over the posterior surface of the duodenum and enters the great omentum, in which it runs to the left, parallel with the greater curvature of the stomach. It gives branches to the latter and to the omentum and forms an anastomotic arch with the left gastro-epiploic artery. The pancreatico-duodenal artery (A. pancreaticoduodenalis) divides into pancreatic and duodenal branches. The former (Ramus pancreaticus) supplies the middle part of the pancreas and is often replaced by a number of variable twigs. The duodenal branch (Ramus duodenalis) passes to the right along the lesser curvature of the duodenum and anastomoses with the first branch of the anterior mesenteric artery.

3. The splenic artery (A. lienalis) is the largest branch of the cœliac. It passes to the left (with the large satellite vein) on the left extremity of the pancreas and across the saccus cæcus of the stomach. Entering the suspensory ligament of the spleen, it runs in the hilus of the spleen to the apex, beyond which it is continued as the left gastro-epiploic. It gives off the following branches:

(a) Pancreatic branches (Rami pancreatici) to the left extremity of the pancreas.

(b) Splenic branches (Rami lienales), which plunge into the substance of the spleen.

(c) Gastric branches (Aa. gastricæ breves), which pass in the gastro-splenic omentum to the greater curvature of the stomach, where they bifurcate and anastomose with the gastric arteries.

(d) The left gastro-epiploic artery (A. gastroepiploica sinistra) is the continuation of the splenic artery. It passes to the right in the great omentum, parallel with the greater curvature of the stomach, and anastomoses with the right gastro-epiploic. It gives off branches to the greater curvature of the stomach, and twigs to the omentum.

II. The anterior or great mesenteric artery (A. mesenterica cranialis) arises from the ventral face of the aorta at the first lumbar vertebra. It is a large unpaired trunk, about an inch (ca. 2 to 3 cm.) in length, which passes ventrally between the vena cava and the left adrenal into the root of the great mesentery, when it divides into three branches—left, right, and anterior.

1. The left branch gives off at once about fifteen to twenty arteries of the small intestine (Aa. intestinales). These come off close together and pass in divergent fashion between the layers of the great mesentery, each dividing into two branches which anastomose with adjacent branches to form a series of arches. In the anterior part of the series secondary arches are formed by the union of branches given off from the primary set of arches. From the convex side of these arches terminal branches pass to the wall of the small intestine, in which they ramify and form a vascular network. They are accompanied by satellite veins and by nerves and lymph vessels. The first artery anastomoses with the pancreatico-duodenal, and the last with the ileal branch of the great mesenteric artery. Branches are supplied to the mesenteric lymph glands.

2. The right branch (A. ileo-cæco-colica) might be regarded as the continuation of the trunk. It runs downward and a little forward and to the right and gives off the ileal, the two cæcal, and the ventral colic arteries.

(1) The ileal or ileo-cæcal artery (A. ilea) passes in retrograde fashion along the terminal part of the ileum and unites with the last branch of the left division.

(2) The external or inferior cæcal artery (Ramus cæcalis lateralis) passes between the cæcum and the origin of the colon and runs on the external muscular band of the cæcum to the apex, where it anastomoses with the internal artery. Besides numerous collaterals to the cæcum, it gives off the artery of the arch, which passes along the lesser curvature of the base of the cæcum and runs on the outer face of the origin of the great colon.

(3) The internal or superior cæcal artery (Ramus cæcalis medialis) passes along the inner band to the apex of the cæcum, where it anastomoses with the external cæcal artery.

(4) The ventral, right, or direct colic artery (A. colica ventralis) runs along the opposed surfaces of the ventral (first and second) parts of the great colon to the pelvic flexure, where it unites with the dorsal colic artery. It supplies the ventral parts of the great colon and sends a branch to the base of the cæcum.

3. The anterior branch divides after a very short course into the dorsal and middle colic arteries.

(1) The dorsal, left, or retrograde colic artery (A. colica dorsalis) is a large vessel which passes along the dorsal (fourth and third) parts of the great colon to the pelvic flexure, where it joins the ventral colic artery.

(2) The middle colic artery or first artery of the small colon (A. colica media) is a much smaller vessel which passes to the origin of the small colon, enters the colic mesentery, and forms an arch by joining the first branch of the posterior mesenteric artery close to the lesser curvature of the bowel. It sends an anastomotic branch to the dorsal colic artery.

III. The renal arteries (Aa. renales), 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 passes directly outward to the kidney and is then disposed like the right one. Small collateral branches are supplied to the ureters and the adrenals. The 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 ventral face of the aorta at the fourth lumbar vertebra, i. e., 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 posterior branch or anterior hæmorrhoidal artery (A. hæmorrhoidalis cranialis) passes backward in the upper part of the mesentery and the mesorectum and terminates near the anus by anastomosing with the internal pudic artery. Three or four of its anterior collateral branches form arches.

V. The spermatic arteries (Aa. spermaticæ internæ), 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 flexuous 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 flexuous 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 flexuous 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 corresponding branch of an aortic intercostal artery. The ventral branch (Ramus ventralis) runs outward in the intertransverse space, passes between the transversus and obliquus internus abdominis, gives branches to these muscles, and ends in the obliquus externus, the panniculus, and the skin of the flank.