Anastomoses.—The intercostal arteries have a chain of anastomoses with each other by communicating branches which cross the heads of the ribs. By this means the superior freely communicate with the subclavian by its inter costal artery. Inferiorly, their anastomosis with the phrenic, circumflex ilii, and lumbar arteries, is equally free ; internally they anasto mose with the arteries of the spinal cord, and in front with the internal mammary and epi gastric.
III. Branches of the abdominal aorta.— They may be divided into anterior and lateral. The anterior branches are, the inferior phrenic, calico., superior and inferior mesenteric.
Phrentc arteries.—The phrenic arteries are two in number; they arise from the aorta im mediately after its entrance into the abdomen, generally distinct, sometimes from a common trunk, and occasionally one or both arise from the coeliac artery, or one of its branches. Each phrenic artery passes outwards in front of the crus of the diaphragm, and along the upper edge of the renal capsule of its own side. The right artery passes behind the vena cava, and the left behind the oesophagus. They run on the abdominal surface of the diaphragm, and at the posterior edge of the cordiform tendon each vessel divides into an external and an anterior branch. The external branch supplies the fleshy substance of the ala of the diaphragm, and sends several branches towards the external attachments of that muscle which anastomose with the lower intercostal and lumbar arteries ; while the anterior branch, coursing round the margin of the cordiform tendon, supplies the anterior part of the diaphragm, and anastomoses with its fellow of the opposite side, behind the ensiform cartilage, sending forwards branches to anastomose with the internal mammary.
Minute branches are given off by the phrenic arteries near their origins to the semilunar ganglia and renal capsules : a small twig from the right phrenic ascends along the vena cava through the diaphragm to anastomose with the comes nervi phrenici of the internal mammary. Another similar twig, given to the oesophagus by the left phrenic, while passing behind that tube, anastomoses with the middle oesophageal arteries.
The coeliac artery, called, also, coeliac axis, is one of the largest and shortest of the vessels given off by the abdominal aorta. It generally
arises from the aorta, between the crura of the diaphragm opposite ,the junction of the last dorsal and first abdominal vertebra, having the renal capsules and semilunar ganglia on either side of it, with the lobulus Spigelii to the right, the cardiac orifice of the stomach to the left, the superior border of the pancreas inferiorly, and the stomach and lesser omentum in front : it is closely embraced by branches of the solar plexus.
The coeliac artery, which is often scarcely half an inch in length, immediately divides into three branches, the gastric or coronaria superior ventriculi, the hepatic, and the splenic, which constitute the tripod of Haller. Sometimes the coeliac axis gives off the phrenic and superior capsular.
Coronary artery of the stomach.—The coro nary artery is the smallest of the three branches furnished by the trunk of the coeliac; it some times arises from the aorta itself. Passing upwards, forwards, and to the left, it arrives at the cardiac orifice of the stomach, from which it proceeds forwards and to the right, following the direction of the lesser arch of the stomach until it arrives near the pylorus, where it anastomoses with the pyloric branch of the hepatic. When the coronary artery has arrived at the cardiac orifice of the stomach, it sends one or -more branches upwards along the oesophagus which supply that part with blood, and anastomose with the oesophageal arteries from the thoracic aorta : it then sends branches round the cardiac orifice, which nearly encircle that part, and ramify over the great extremity of the stomach, where they anastomose with the vasa brevia of the splenic. In its course along the lesser arch of the stomach the coronary sends many branches over both surfaces of that viscus, which anastomose with each other and with the right and left gastro-epiploic. The ter minal branch of the coronary which ends at the pylorus is sometimes called superior pyloric. Sometimes the coronary artery gives off the right hepatic immediately before reaching the cardiac orifice of the stomach.