54 LABORATORY DIRECTIONS 



forward as the ventral aorta, which gives off afferent branchial 

 arteries to the gills. These will be traced later. 



The auricle is a thin-walled sac dorsal to the ventricle. It 

 contains a single cavity that leads to the ventricle. Lift up the 

 ventricle and find the sinus venosus that lies just anterior to 

 the transverse septum. It brings blood from the veins and 

 empties into the auricle. 



Veins. — In the preparation of the specimen the arteries were 

 injected with a colored substance to make them stand out more 

 clearly. The veins, however, have not been so treated and 

 will appear dark with clotted blood, or in some cases may be 

 colorless. 



The veins are best dissected by beginning at the sinus venosus 

 and tracing them backward. They are thin-walled and in places 

 dilate to form sinuses. Make a transverse incision across the 

 ventral wall of the sinus venosus. Wash out any clotted blood. 

 Spread the walls apart and look for the openings of vessels into 

 the sinus. In the posterior region near the median line find 

 the apertures of the hepatic sinuses. Stick probes into them and 

 follow the probes back into the liver and expose these large liver 

 sinuses. 



Entering the sinus venosus from the lateral sides are the large 

 ducts of Cuvier. These continue partially around the oesophagus 

 and end in the anterior and posterior cardinal sinuses, which 

 extend respectively toward the head and toward the tail. The 

 posterior cardinal sinuses are a pair of very large vessels lying side 

 by side along the dorsal wall of the body cavity. Posteriorly 

 they narrow down and extend between the kidneys. Numer- 

 ous renal veins may be seen entering the posterior cardinals. 

 Each anterior cardinal sinus extends dorsal to the gill arches in 

 the direction of the eye, where it connects with a large orbital 

 sinus. The anterior cardinal sinus Is best dissected by making 

 an incision dorsal to the gills and when the sinus is located 

 tracing It each way. 



Entering each posterior cardinal sinus is a subclavian vein 

 which brings blood from the pectoral fin, and a lateral vein which 

 extends along the lateral side of the abdominal cavity from pelvic 

 to pectoral regions. (The lateral veins may have been removed 

 in opening the shark.) The two lateral veins are connected in 



