28 THE SKATE 



All of the systemic veins carry blood to this common car- 

 dinal vein. 



There is a slight fold at the juncture of the sinus and the 

 common cardinal vein near which is the rather small en- 

 trance of the inferior jugxdar, a vein which collects blood 

 from the walls of the pericardial cavity and the floor of 

 the mouth and pharyngeal cavities. Use a bristle to probe 

 into it. The hepatic sinus enters through the posterior wall 

 of the common cardinal. Its main chamber is a large space 

 situated between the anterior end of the liver and the 

 transverse septum. Locate this chamber and cut it open. 

 It has an outlet towards both right and left common car- 

 dinal veins. Several small hepatic veins enter it from the 

 liver. 



The pericardio-peritoneal canal runs through the center 

 of this sinus. It will be remembered that this canal con- 

 nects the two otherwise separated parts of the coelom. 

 Kefer back to Chapter IV. 



The posterior cardinal vein enters the common cardinal 

 through the dorsal part of the posterior wall. Probe into 

 this part of the common cardinal and towards the midline 

 of the dorsal wall of the pleuroperitoneal cavity. The 

 posterior cardinal continues as a large space located on 

 the dorsal side of the testes in the male and on the dorsal 

 side of the oviduct in the female. Posteriorly it will be 

 found to unite with the one from the other side, forming 

 a median sinus which is directly connected through its 

 ventral walls with the genital sinus. The latter originates 

 as large spaces about the gonads. The median sinus sepa- 

 rates again posteriorly into two veins proceeding on the 

 medial side of the kidneys, where they are again united. 



The anterior cardinal sinuses return the blood from the 

 anterior part of the body and head. Eun the probe from 

 the common cardinal towards the dorsal side of the skate, 



