VASCULAR SYSTEM 



25: 



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 Ceratodus 

 at all events, an anterior abdominal vein 

 opens into the right ductus Cuvieri ; 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 (Gunther [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 

 remains on each side, leading into the 

 modified tubular region of the kidneys, 

 which meet in the middle line. The 

 Mtillerian ducts persist to a great extent 

 in the adult male Dipnoi, opening in- 

 dependently into the cloaca. The eggs, 



■2-2:5. 



Diagram of the venous system 

 of Protopterus anne.ctens, Owen, 

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

 as, anastomosis between posterior 

 cardinals ; c, conus ; c.v, caudal 

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

 portal vein ; h.v, hepatic vein ; i, 

 intestine ; i.j, inferior jugular vein ; 

 .7, jugular vein ; k, kidney ; I, liver ; 

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

 otrium ; oes, oesophagus ; o.r, 

 ovarian vein ; p, pericardium ; p.v, 

 parietal vein ; r.p, renal portal ; 

 r.p.c, right posterior cardinal ; set, 

 subclavian vein ; st, stomach ; v, 

 ventricle ; v.c, vena cava. 



