200 



THE ELASMOBRANCH FISHES 



VEINS FROM KIDNEY OR MESONEPHROS 



Blood is returned from the kidneys and the back by the two large postcardinal 

 veins {p.c, fig. 185) which run along the sides of the spinal column just under 

 the lining of the body cavity. The right one of these veins may be traced as 

 a single vessel from the posterior tip of the kidney forward to the region of 



the inferior mesenteric artery, where it 

 is joined by the left postcardinal. Just 

 behind the origin of the posterior in- 

 testinal artery the two postcardinals in 

 Heptanchus are joined by two or more 

 cross-trunks (dr.). 



The postcardinals receive numerous 

 revehentes {rv., fig. 186b) from the kid- 

 ney, which have collected the blood dis- 

 tributed by the advehentes (av., fig. 

 186a) of the renal portal veins. As the 

 two postcardinals pass forward they 

 receive segmental veins from the body 

 wall and before reaching the heart in- 

 crease in size to form the enlarged post- 

 cardinal sinuses (p.c.s., fig. 185). The 

 walls of right and left sinuses freely 

 intercommunicate posteriorly and an- 

 teriorly and are held in place by multi- 

 tudes of tendinous cords. The posterior 

 cardinals enter the duct of Cuvier {d.c, 

 fig. 183) posterior and mediad of the 

 aperture for the anterior cardinal sinus. 



Fig. 184. Diagram of inferior jugular 

 vein, Heptanclnts maculatus. (Mast Wolf- 

 sohn, orig.) 



CO., coracoid cartilage ; h.s., liyoidean 

 vein or sinus; hy.af., hyoidean afferent 

 artery; i.j., inferior jugular vein; nu., 

 nutrient vein ; smt., submental vein ; tli., 

 thyroid gland; th.v., thyroid vein; v.a., 

 ventral aorta. 



VEINS FROM DIGESTIVE TRACT 



Venous blood is returned from the di- 

 gestive tract to the heart by the hepatic 

 portal system of veins (see fig. 155, 

 /«.?;., facing p. 166) .The principal veins 

 making up this system in Heptanchus are : the posterior intestinal, the intrain- 

 testinal, the anterior intestinal, the gastrics, the portal, and the hepatic veins. 

 The posterior intestinal vein, as the dorsal intestinal {d.i.v., fig. 155), drains 

 the rectal gland and passes forward along the colon and valvular intestine. 

 At about the place where the posterior intestinal artery (p.i.a.) reaches the 

 valvular intestine the vein, as the posterior intestinal proper, leaves the in- 

 testine and passes over the bridge of the pancreas. Before joining the anterior 

 intestinal vein it receives the large anterior gastro-pancreaticosplenic vein 

 formed by a gastric branch from the dorsal side of the cardiac stomach, splenic 



