208 



THE ELASMOBRANCH FISHES 



terior from this vessel in both Scyllium and Raja is the dorsal myelonal vein 

 (my.). This vein is absent, however, in Acanthias (fig. 181). A ventral 

 myelonal vein, arising posterior to the optic chiasma, drains the vascular sacs 

 and passes on down the cord. 



The hyoidean vein in Mustelus enlarges ventrall}' into the hyoid sinus. Each 

 sinus (h.s., figs. 190 and 193) is triangular and of large size, the base of the 



triangle extending from the tip of the 

 lower jaw in front to back of the first 

 afferent artery. In Acanthias the fore- 

 most of the communicating vessels be- 

 tween right and left hyoidean veins 

 forms the hyoidean sinus. In Car- 

 charias and Raja a thyroidean sinus of 

 considerable size is formed in the mid- 

 line ventral to the thyroid gland (Fer- 

 guson, 1911). 



From the postero ventral angle of the 

 hyoidean sinus, the inferior jugular 

 vein passes backward to enter the duct 

 of Cuvier (figs. 190 and 193). On its 

 way it receives the ventral nutrient 

 veins (nu.) which are connected with 

 the dorsal nutrients of the anterior car- 

 dinal sinus. 



EENAL PORTAL SYSTEM 



In the embryonic condition a su])intes- 

 tinal vein extends from the tail to the 

 heart. It later separates into an ante- 

 rior and a posterior part, the anterior 

 part becoming the line of the hepatic 

 portal system and the posterior part 

 that of the renal portal system now 

 under consideration. 



The caudal vein, as the basis of the 

 renal portal system of the adult, ex- 

 tends from the tip of the caudal fin through the haemal canal to the cloaca. 

 It represents the stem of a Y, the arms of which pass to the sides of the cloaca 

 as the renal portal veins (r.p., fig. 194a) . Each renal portal continues forward 

 and upward dorsal to and along the lateral margin of the kidneys, giving to 

 each numerous advehentes. 



In its course as a single median vessel, the caudal receives dorsal and ven- 

 tral segmental veins on each side, which are of large size at the place where the 

 dorsal and ventral lobes of the fin are deepest. The two renal portals also re- 

 ceive segmental veins from the body wall in the region of the kidneys and from 



Fig. 193. Veins ventral to pharynx, Mus- 

 telus antarticus. (From T. J. Parker.) 



a.c.s., anterior cardinal sinus; hr.v., 

 brachial vein; li.s., hyoid sinus; h.v., hyoi- 

 dean vein; i.j., inferior jugular; l.a.v., 

 lateral abdominal vein; nu., nutrient; 

 p.c.s., postcardinal sinus. 



