BRANCHES OF THE ABDOMINAL AORTA. 229 



the aorta. As the latter terminates at the fourth lumbar verte- 

 bra, the fifth lumbar artery is a branch from the fourth in most 

 instances. *^ 



At the base of the transverse process each artery divides into 

 two branches, a posterior or dorsal one, and an anterior or 

 lumbar. The dorsal branch, which is smaller than the other, 

 detaches a ramification through the intervertebral foramen to 

 the lower part of the medulla spinalis and to the cauda equina: 

 it then gets to the back, where it is spent upon the muscles near 

 the spine. The anterior lumbar branch advances between the 

 broad muscles of the abdomen, to which it is distributed; and 

 runs forwards far enough to anastomose with the epigastric 

 artery. 



The first lumbar artery is small, and sometimes comes from 

 the last intercostal; it goes a little below the inferior margin of 

 the last rib, and then descends almost vertically between the pe- 

 ritoneum and the transversus abdominis muscle. The lower 

 lumbar arteries anastomose with the circumflexa ilii, and with 

 the superficial branches of the gluteal. 



The Middle Sacral Artery (Arteria Sacra Media) is generally 

 not so large as a lumbar; it arises from the centre of the bifur- 

 cation of the aorta into the two primitive iliacs, or else a line or 

 two above it, behind. It descends, in front of the middle line of 

 the fifth lumbar vertebra and of the sacrum, to the coccyx, 

 adhering to the surface of these bones, and performing some 

 flexuosities. 



It sometimes happens that the last pair of lumbar arteries 

 come from it, or at least one, according to Meckel, more com- 

 monly the left: in which case the sacral is of unusual size. The 

 sacral afterwards sends off", to the right and left, a pair of 

 branches for each pair of sacral foramina. They run across the 

 sacrum, send branches to it, anastomose with the lateral sacral 

 arteries, and then penetrate to the cauda equina. The middle 

 sacral artery is lost at the inferior end of the coccyx, in the fat 

 and cellular tissue of the part. 



VOL. 1121 



