THE PHRENIC AND LUMBAR ARTERIES. 467 



B.-PABIETAL BRANCHES OF THE ABDOMINAL AORTA. 



Inferior phrenic arteries (v). The inferior phrenic or diaphragmatic 

 arteries are two small vessels, which arise, either separately or by a short common 

 trunk, from the aorta on a level with the upper margin of its orifice in the dia- 

 phragm, or from one of the upper branches of the aorta, most frequently the coeliac 

 axis. They soon diverge from each other, and, passing across the crura of the 

 diaphragm, incline upwards and outwards on its under surface, the artery of the 

 left side passing behind the oesophagus, while that of the right side passes behind 

 the vena cava. Before reaching the central tendon of the diaphragm, each of 

 the arteries divides into two branches, of which one runs forwards towards the 

 anterior margin of the thorax, and anastomoses with the corresponding artery 

 of the opposite side, and with the superior phrenic and musculo-phrenic branches 

 of the internal mammary artery, while the other pursues a transverse direction 

 towards the side of the thorax, and communicates with offsets of the lower inter- 

 costal arteries. 



Besides supplying the diaphragm, each phrenic artery gives small branches 

 (superior suprarenal) to the suprarenal body of its own side ; the left artery sends 

 some branches to the oesophagus, which anastomose with the other oesophageal 

 arteries ; and the artery of the right side gives some twigs to the upper part of the 

 vena cava. Small offsets pass also to the liver between the layers of the peritoneum, 

 and anastomose with branches of the hepatic artery. 



Varieties. The phrenic arteries vary greatly in their mode of origin, bub these deviations 

 seem to have little influence on their course and distribution. In the first place they may 

 arise either separately, or by a common trunk ; and it would appear that the latter mode of 

 origin is nearly as frequent as the former. When the two arteries are joined at their origin, 

 the common trunk arises most frequently from the aorta ; though, sometimes, it springs 

 from the coeliac axis. When arising separately, the phrenic arteries are given off sometimes 

 from the aorta, more frequently from the coeliac axis, and occasionally from the coronary 

 artery of the stomach, or the renal ; but it most commonly happens that the artery of the 

 right side is derived from one, and that of the left side from another of these sources. One 

 artery has also been seen arising from the superior mesenteric. In only one out of thirty-six 

 cases observed by R. Quain did these arteries arise as two separate vessels from the abdominal 

 aorta. An additional phrenic artery, derived from the left hepatic, has been met with 

 (R. Quain). 



Lumbar arteries (iv-v). The lumbar' arteries resemble the intercostal 

 arteries, not only in their mode of origin, but also in a great measure in the manner 

 of their distribution. They arise from the back part of the aorta, and are usually 

 five in number on each side. They pass outwards, the first one over the body of 

 the last dorsal vertebra, while the others rest on the upper four lumbar vertebras, 

 and soon dip deeply under the psoas muscle. The upper arteries are likewise behind 

 the pillars of the diaphragm ; and those on the right side are covered by the vena 

 cava. At the interval between the transverse processes, each lumbar artery divides 

 into an abdominal and a dorsal branch. 



Branches. (a) The abdominal branch runs outwards, generally behind the 

 quadra tus lumborum, but that of the first artery passes in front of this muscle with 

 the anterior division of the last dorsal nerve, and a similar position is not unfre- 

 quently taken by one or two of the lower ones. Continuing outwards between the 

 abdominal muscles, the vessel ramifies in their substance, and the several arteries 

 form anastomoses with one another, with the branches of the epigastric and 

 internal mammary in front, with the terminal branches of the lowest intercostals 

 above, and with offsets of the ilio-lumbar and circumflex iliac arteries below. 



(b) The dorsal branch, like the posterior branch of an intercostal artery, gives 

 off immediately after its origin an offset to the spinal canal, and then, proceeding 



VOL. II. H H 



