BLOOD-VASCULAR SYSTEM OF THE LORICATI IO9 



Mes.V.). This vessel arises from 2 good sized branches 

 designated as Y and Z (see fig. i). Branch Z which is strictly 

 a gastric vein, takes its origin from several branches coming 

 from the posterior or cardiac end of the stomach ; one of which 

 anastomoses with the right gastric vein ; and 2 other branches 

 anastomose with branches of the left gastric and posterior gas- 

 tric veins. The course of branch Z is dorso-caudad ; passing to 

 the left of the intestine and its vessels, it unites with branch Y 

 directly below the reproductive organs. Branch Y, which is 

 distinctly an intestinal vein, drains the posterior end of the 

 intestine, and usually anastomoses with intestinal vein^,); pass- 

 ing caudad it joins branch Z in forming the main posterior gas- 

 tric stem, which passes between the reproductive organs, with- 

 out receiving any branches, penetrates the posterior ventral 

 surface of the kidney, and passing to the left of the right 

 cardinal empties into the renal portal vein. It would be possible 

 for the blood in the posterior mesenteric to flow in either direc- 

 tion, but it is probable that the least resistance is toward the 

 kidney. 



After receiving the posterior mesenteric vein the caudal or 

 renal portal vein bifurcates into a right and a left renal portal 

 vein or vena renalis advehens (figs, i and 10; Ren.P.V.). 

 These trunks run cephalad for some little distance through the 

 dorso-lateral part of the kidney, and gradually decrease in 

 caliber by giving off numerous ventral branches, the afferent 

 renal veins or venae renales advehentes (figs, i and 10, 

 A. Ren. v.). These vessels break up into rather coarse venous 

 capillaries near the lateral surface of the kidney, and become 

 collected ventrad and mesad by the small efferent renal veins 

 or venae renales revehentes (figs, i and 10 ; E.Ren.V.). A 

 cross section through an injected kidney hardened in formalin 

 shows us that these vessels, many of which are visible from the 

 ventral side of the kidney, empty into the right cardinal from 

 every direction. 



(3) The right cardinal vein (PI. I, figs, i, 5 and 10; 

 R.Car.V.), which is the principal cardinal has its source 

 mainly from the efferent renal veins ; it arises in the extreme 

 caudal end of the kidney, below the caudal vein, and passes 



