BRANCHES OF THE ABDOMINAL AORTA. 309 



thyroid arteries ; and the inferior with similar branches of the phrenic and 

 gastric arteries. 



The INTERCOSTAL, or posterior intercostal arteries, arise from the poste 

 rior part of the aorta ; they are nine in number on each side, the two su 

 perior spaces being supplied by the superior intercostal artery, a branch 

 of the subclavian. The right intercostals are longer than the left, on ac- 

 count of the position of the aorta. They ascend somewhat obliquely from 

 their origin, and cross the vertebral column behind the thoracic duct, vena 

 azygos major, and sympathetic nerve, to the intercostal spaces, the left 

 pacing beneath the superior intercostal vein, the vena azygos minor and 

 sympathetic. In the intercostal spaces, or rather, upon the external inter- 

 costal muscles, each artery gives off a dorsal branch, which passes back 

 between the transverse processes of the vertebrae, lying internally to the 

 middle costo-transverse ligament, and divides into a spinal branch, which 

 supplies the spinal cord and vertebrae, and a muscular branch which is 

 distributed to the muscles and integument of the back. The artery then 

 comes into relation with its vein and nerve, the former being above and 

 the latter below, and divides into two branches which run along the bor- 

 ders of contiguous ribs between the two planes of intercostal muscles, and 

 anastomose with the anterior intercostal arteries, branches of the internal 

 mammary. The branch corresponding with the lower border of each rib 

 is the larger of the two. They are protected from pressure during the 

 action of the intercostal muscles, by little tendinous arches thrown across 

 them and attached by each extremity to the bone. 



BRANCHES OF THE ABDOMINAL AORTA. 



Phrenic, 



C Gastric, 

 Coeliac axis < Hepatic, 



( Splenic. 



Superior mesenteric, 

 Spermatic, 

 Inferior mesenteric, 

 Supra- renal, 

 Renal, 

 Lumbar, 

 Sacra media. 



The PHRENIC ARTERIES are given off from the anterior part of the aorta 

 as soon as that trunk has passed through the aortic opening. Passing 

 obliquely outwards upon the under surface of the diaphragm, each artery 

 divides into two branches, an internal branch, which runs forwards, and 

 inosculates with its fellow of the opposite side in front of the oesophag'-al 

 opening ; and an external branch, which proceeds outwards towards the 

 great circumference of the muscle, and sends branches to the supra-renal 

 capsules. The phrenic arteries inosculate with branches of the internal 

 mammary, inferior intercostal, epigastric, cesophageal, gastric, hepatic, and 

 supra-renal arteries. They are not unfrequently derived from the coeliac 

 axis, or from one of its divisions, and sometimes they give off the supra- 

 renal arteries. 



