3. A. lienalis (f).—The splenic artery is the largest of the branches of the cœliac axis, of which it appears to be the direct continuation. It divides into two large branches, one to the cranial end, the other to the caudal end, of the spleen (1). From the latter a large branch passes to the pancreas and descending limb of the great omentum.
B. A. mesenterica superior ([Fig. 126], d).—The superior mesenteric artery is larger than the cœliac. It supplies the blood to the small intestines and caudal portion of the pancreas and to the ascending and transverse colon. It arises from the ventral side of the abdominal aorta about one centimeter caudad of the cœliac axis and passes caudoventrad, forming a curve with the convexity dextrad. It gives off the pancreaticoduodenalis inferior, colica media, colica dextra, ileocolica, and numerous branches to the small intestine.
1. A. pancreaticoduodenalis inferior ([Fig. 125], k).—This passes to the caudal end of the pancreas and a part of the duodenum, anastomosing with the pancreaticoduodenalis superior.
2. A. colica media is a large branch to the transverse and descending portions of the large intestine. It divides and sends branches in both directions which anastomose with the colica dextra and with branches from the inferior mesenteric arteries.
3. A. colica dextra.—A small branch which passes to the ascending and transverse colon, anastomosing with the colica media and ileocolica. It is sometimes absent.
4. A. ileocolica.—This passes to the cæcum and supplies that structure, sending branches to the ileocolic valve and the caudal end of the ileum, and anastomosing with the colica dextra and the intestinal branches of the superior mesenteric.
5. The superior mesenteric now divides into about sixteen terminal branches which pass to the small intestine. In many cases these branches unite near the intestine, forming arches, and from these arches numerous short branches pass to the intestine.
3. A. adrenolumbalis (or lumboabdominalis) ([Fig. 126], e).—This rises from the aorta, one on each side, about two centimeters caudad of the superior mesenteric. Each passes laterad onto the dorsal body wall, supplying the muscles of this region. A large branch passes caudad along the surface of the muscles dorsad of the kidney and anastomoses with the iliolumbar artery. From the adrenolumbalis rises usually:
A. phrenica (f).—The phrenic artery rises either from the cœliac (c) or the adrenolumbalis (e) and passes to the diaphragm, near its dorsal border. In the diaphragm it passes ventrad, lying at the medial margin of the costal portion of the diaphragm, as far as its sternal portion, where it unites with the artery of the opposite side. The two thus form an arch, from which radiating arteries pass off to supply the diaphragm.
4. A. renalis (g).—The two renal arteries arise from the sides of the aorta, usually at about the same point, so that the left passes caudolaterad and the right craniolaterad (owing to the position of the kidneys). The artery usually divides just before entering the kidney (2). It passes dorsad of the vein (t). The renal artery sometimes sends a branch to the suprarenal body (1). It also occasionally gives origin to the spermatic artery (h).