424 COMPARATIVE ANATOMY 



FIG. 327. DIAGRAM OF THE VEINS OF AN ELASMOBRANCH. From the ventral 



side. 



Card. ant. (Jug], anterior cardinal (jugular) ; the inferior jugular is seen nearer 

 the middle line; Card.V.S, cardinal sinus, communicating with its 

 fellow in the middle line ; Caud.i, caudal vein, which divides into two 

 renal portals, A, A 1 , at the posterior end of the kidneys (N) : from 

 these arise the advehent veins of the renal portal system (V.adv) 

 Duct. Guv, precaval sinus; Gen.V, genital veins; H, heart; Leb, liver; 

 L.V.S, hepatic sinus; Seit.V, lateral vein, into which open a venous 

 network in the region of the cloaca (Ven.CLB), one or more cutaneous 

 veins of the tail (Cut. V), and veins from the body-walls and pelvic fins (HEV) ; 

 Sitbcl, subclavian ; V.port, hepatic portal vein, receiving its blood from 

 the intestine (ED), stomach (Mg), and oesophagus (Oes. V), and anastomosing 

 with the lateral vein posteriorly and with the cardinal sinus anteriorly ; 

 V.rev, revehent renal veins, from which the posterior cardinals (CV) arise ; 

 t, anastomosis between portal and systemic veins. 



the hepatic veins, which open into the sinus venosus. New vessels 

 from the various parts of the alimentary canal (gastric, splenic, 

 and mesenteric veins) are gradually developed, the pre-caudal 

 portion of the subintestinal vein becoming of minor importance ; 

 all these vessels unite to form what is now known as the hepatic 

 portal vein, and thus pour their blood through the capillaries 

 of the liver (Figs. 325-329, and 331). 



Anteriorly to the heart, a paired precaval vein (ductus Cuvieri) 

 is developed, and opens into the sinus venosus. This is formed, 

 on either side, by the confluence of an anterior and a posterior 

 cardinal vein, the former bringing back the blood from the head 

 (external and internal jugulars), and the latter from the body, 

 in which it runs on either side of the aorta, between the latter 

 and the kidneys. A paired inferior jugular from the' ventral part 

 of the head into which the nutrient branchial veins open, also 

 communicates with the precaval. A suMavian vein from the 

 pectoral fin also enters to the precaval sinus or proximal end of 

 the posterior cardinal vein. 



The caudal vein usually bifurcates posteriorly to the cloaca, each 

 branch passing along the outer side of the corresponding kidney, 

 and giving off advehent vessels into the latter. These divide 

 up into capillaries, forming a renal portal system, the capillaries 

 again uniting to form revehent veins which open into the posterior 

 cardinals. Thus the condition of the veins typical of adult 

 Fishes is reached, and a few of the more important modifications 

 must now be briefly referred to. 



In Cyclostomes, Elasmobranchs, and Dipnoans, the anterior 

 part of the subintestinal vein still persists as a small vessel 

 running within the spiral valve of the intestine. In the Elasmo- 

 branchs, many of the veins (e.g., precavals, anterior and posterior 

 cardinals, inferior jugulars, hepatic and genital veins) enlarge 

 to form capacious sinuses, and a large lateral vein (Figs. 325, 327), 

 running in the body- walls, opens into each precaval or posterior 

 cardinal. This probably corresponds to the vein of the primary 

 lateral-fin folds (p. 137). 



