VASCULAR SYSTEM 



253 



mentioned above. Secondly, the right posterior cardinal is interrupted 



in front, and contributes to the formation 



of a posterior vena cava, carrying blood 



from the caudal vein and kidney directly 



to the sinus venosus. Thirdly, in Cemtodus 



at all events, an anterior abdominal vein 



opens into the right ductus Cu'vieri ; it 



is formed by the junction of two pelvic 



veins, themselves derived from iliac and 



renal portal veins. This epigastric, or 



anterior abdominal vein, so amphibian in 



appearance, is probably homologous with 



the lateral veins of Elasmobranchs. 



The kidneys, the gonads, and their 

 ducts differ but little in Ceratodus from 

 those of other primitive fish, such as the 

 Elasmobranchs (Giinther [190], Semon 

 [402-3], Kerr [260-61], Parker [324]). 

 An elongated mesonephros, which loses 

 its coelomic funnels in the adult, pours 

 its secretion into a duct opening into a 

 median cloacal caecum. The caecum, 

 derived from the fused bases of the 

 ducts, is placed above the rectum. Long 

 oviducts, in the female, having open 

 funnels in the front region of the 

 abdominal cavity, pass back to open into 

 the cloaca (Fig. 355). 



In the male Ceratodus the semen is 

 carried by numerous vasa efferentia into 

 the kidney, passes through certain of the 

 renal capsules and tubules to the meso- 

 nephric duct, and thereby reaches the 

 cloaca (Fig. 356). 



Lepidosiren is more specialised in that 

 the vasa efferentia are few in number, 

 arise from a sterile tubular posterior 

 portion of the testis, and pass into the 

 posterior region of the kidney. Finally, 

 in Protopterus one vas efferens alone 



plv. 



FIG. 223. 



Diagram of the venous systent 

 of Protopterus annectens, Owen, 

 ventral view. (After W. N. Parker.)' 

 us, anastomosis between posterior 

 cardinals; c, conns; u.v, caudal 

 vein ; g.b, gall-bladder ; h.p, hepatic 

 remains On each Side, leading into the portal vein ; h.v, hepatic vein ; i, 

 TC j , i i e ,i i i intestine ; i. j, inferior jugular vein ; 



modified tubular region of the kidneys, j, jugular vein ; k, kidney ; i, liver j. 



l.p.c, left posterior cardinal ; o, 

 otrium ; oes, oesophagus ; o.v, 

 ovarian vein ; p, pericardium ; p.v, 



,, i T\- parietal vein; r.p, renal portal; 



111 the adult male Dipnoi, Opening in- r.p.e, right posterior cardinal 



which meet in the middle line. The 

 Miillerian ducts persist to a great extent 



dependently into the cloaca. 



pcrcrc 

 eg o S, 



scl, 



subclavian "vein ; st, stomach ; r, 

 ventricle ; v.c, vena cava. 



