VASCULAR SYSTEM 



317 



their extent they are embedded in the Iddneys (Fig. 186) ; and in 



this region the two veins are in close relation in the median line, 



and here and there freely communicate with each other. More 



anteriorly, they enlarge so much 



that they present the appearance 



of cavernous sinuses. In addition 



to the anterior segmental and ovi- 



ducal veins, the posterior cardinals 



receive the spermatic or the ovarian 



vein from the male or female 



gonad. 



The precaudal section of the 

 primitive subintestinal vein, now 

 termed the internal intestinal vein 

 (Figs. 186 and 187), traverses the 

 spiral valve as it passes forwards 

 to the hver, but from a physio- 

 logical point of view is now merely 

 one of the factors of the great 

 hepatic portal vein, the principal 

 tributaries of which are the veins 

 from the stomach and intestine, 

 including the rectal gland, and the 

 pancreas and spleen. On entering 



Fig. 186. — Venous system of ilustelus ant- 

 arcticus. a, Auricle ; ax, anterior cardinal ; 

 h.a, conns arteriosus ; br.v, bracliial vein ; 

 c.d, Cuvierian duct or precaval vein ; c.v, 

 caudal vein ; cl.v, cloacal vein ; f.v, femoral 

 vein ; h.s, liyoidean sinus ; h.v, hepatic vein ; 

 i.i.v, internal intestinal vein ; i.j, inferior 

 jugidar ; k, kidney ; I, liver ; l.v, lateral 

 vein ; md.v, mandibular vein ; n.h.v, nutrient 

 liyoidean veins ; o.s, orbital sinus ; p. c, pos- 

 terior cardinal ; p.v, hepatic portal vein ; 

 rp.v, renal portal vein ; sc.v, subscapular 

 vein ; sp.v, spermatic vein ; s.v, sinus 

 venosus ; r, ventricle ; v.a, ventral aorta. 

 (After T. J. Parker.) 



the liver the hepatic portal vein divides into two principal 

 branches for the right and left halves of the gland. From the 

 liver the blood is conveyed by two hepatic veins to the sinus 

 venosus. 



The lateral veins (Fig. 186) are situated in the lateral walls 



