192 JOHN LEWIS BREMER 



man, on the other hand, have neither large Wolffian body nor 

 great curvature ; less marked variations or the accidental blocking 

 of one or the other of the vessels might be expected to determine 

 the adult relations, and anomalies should be frequent and very 

 variable. 



A secondary result of the increased curvature of the rump 

 region is the formation of the a. ilio-lumbalis and a. adreno- 

 lumbalis in the cat, and of similar vessels in the rabbit. These 

 vessels, situated in the lumbar region, are derived from the 

 extension of the periaortic plexus into the area lateral to the 

 aorta, left vacant by the separation of the aorta and the spinal 

 cord. In the thoracic region of these animals and in all regions of 

 other animals this area is supplied by the ventral branches of the 

 dorsal segmental arteries, which are prolonged into the lateral 

 body-wall. But the increasingly dorsal direction of the dorsal 

 arteries, following the increased curvature of the body, causes a 

 sharp angle where the ventral branches leave their dorsal seg- 

 mental trunks, and thus puts the ventral or body-wall branches 

 at a disadvantage, and makes their territory of distribution fall an 

 easy prey to the rapidly growing branches of the plexus with its 

 shorter and more direct lateral roots from the aorta. The re- 

 sulting vessels, as described in the cat by Reighard and Jennings 

 (12), pass in front of the psoas muscles, and after anastomosing 

 with each other (the longitudinal strands of the plexus) send 

 branches to the ventral body muscles. In this region the usual 

 ventral branches of the lumbar arteries are lacking. 



Such vessels to the ventral and lateral body muscles should not 

 be mistaken for the normal lumbar arteries of the adult, which 

 are the dorsal segmental arteries of the embryo. The latter, or 

 true lumbar arteries, pass behind the psoas muscles near to the 

 vertebrae, to which they send branches, and then supply the 

 spinal cord and dorsal muscles on their way to the body-wall. 

 The newer vessels pass in front of the psoas group and are with- 

 out dorsal branches. Because of the connections of both with 

 the body- wall, I think their differences have often been over- 

 looked in the descriptions of the anomalous origin in man of the 

 renal artery from a ' lumbar artery.' 



