VI 



VENOUS SYSTEM 



421 



Tin- anterior abdominal vein arises as ;i pair of sin;ill veins in 

 the ventral body-wall. These unite in trout in the region of the 

 liver and open into the left duct of Cuvier according to Hochstetter. 

 Later the two veins fuse into a single unpaired vessel except at 

 their hinder ends where they become connected with the renal portal 

 vein on each side. Anteriorly the opening into the duct *of Cuvier 

 becomes replaced by an opening into the hepatic portal vein. 



sv. 



a c.i'. 



P.IT.C 



cv. 



r.p. 



B 



Fia. 194. Development of main venous trunks in &il<i,iunulra according to 

 Hochstetter (1888). 



a.c.v, anterior cardinal vein ; e.t>, caudal vein ; <!.<', duct of ('uvicr ; li.r, hepatic vein ; op, opistho- 

 nephros ; P.C.V, posterior cardinal vein: /..r.r. posterior vena cava: pft, pronephric sinus; r.p, renal 

 portal; s, .subclavian ; .--.i.e. sultintcstinal vein ; *.r. sinus venosus. 



SAUROPSIDA. Here we find the same main venous trunks as in 

 the lower groups and, in correlation with the large quantity of yolk, 

 the ventral or vitelline system of veins develops precociously as 

 compared with the dorsal or cardinal system. 



Lacerta, which has been investigated in detail by Hochstetter 

 (1892), may be taken as an example of the Eeptiles. The first veins 

 to make their appearance are the lateral vitelline veins which pass 

 forwards on the dorsal side of the yolk-sac, converging in front to form 



