THE ELASMOBRANCH FISHES 



215 



ventral vessel. Anteriorly, in the embryonic amphibian, it enters tlie duct of 

 Cuvier, but later, by secondary twigs, it comes to empty directly into the liver. 

 From these characteristics it appears likely that the ventral abdominal in 

 Amphibia is homologous with the lateral abdominal of Elasmobranchs. 



VEINS or HEART 



Three sets of vessels return blood, distributed ])y the coronary arteries, from 

 the heart itself. These are a small right coronary, a median cardiac vein, and a 

 larger left coronar}- vein. These veins enter the sinus venosus, near the sinu- 

 auricular opening, usually bj^ two or more apertures. The right and left 

 systems in Acanthias, however, join and empty into the sinus venosus by a 

 single large aperture. 



Fig. 198. Cutaneous system of veins, Squalus sucTclU. (Helen Hopkins, orig. ) 



cd.v., caudal vein; ?.c.f. and l.c.v}, superior and inferior lateral cutaneous veins; 'm.v., 

 median vein; p.c, posteardinal vein; p.d.c, posterior dorsal cutaneous vein ; p.v.c, posterior 

 ventral cutaneous ; s.sc.v., subscapular vein. 



The right coronary may drain the right side of the ventricle and the dorsal 

 side of the conus {Carcharias lit f oralis), emptying into the sinus venosus by 

 its own aperture at the right side of the sinu-auricular opening; or the right 

 may arise as two vessels on the dorsal and ventral sides of the conus and on the 

 ventral side of the ventricle. These two continue separately and open inde- 

 pendently {Raia erinacea). The left coronary in Raia erinacea is of consider- 

 able size and drains the ventral and lateral parts of the ventricle. In other 

 forms it is a vessel of importance {Carcharias littoralis, Cetorhi^ius, Scyl- 

 lium), draining the ventral and lateral parts of the ventricle. 



The cardiac veins drain the dorsal part of the ventricular wall. They may 

 form as a double vessel and unite to enter the sinus venosus with the left 

 coronarj^ {Carcharias littoralis), or they may empty independently into the 

 sinus venosus by a half-dozen smaller mouths {Raja rubens) . In Raia erinacea 

 numerous vessels receive blood from the large triangular area lying parallel 

 to the posterior margin of the sinus venosus and empty it directly into the 

 sinus venosus. 



The vessels of Thebesius in the Elasmobranchs, according to Parker and 

 Davis (1899), are deep in the walls of the heart and are connected with the 

 coronary veins. They may be detected by immersing the heart in water and 



