208 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



meet the incision previously made across the gill slits. The entrance of the 

 common cardinal vein into the sinus is thus slit open. The following may then 

 be noted. In the spiny dogfish just medial to the main opening of the common 

 cardinal vein into the sinus are several small apertures, most of which appear to 

 be subdivisions of the chief opening. The most anterior of these small apertures 

 is, however, the opening of the inferior jugular vein. In the smooth dogfish the 

 accessory openings are lacking, and the entrance of the inferior jugular vein is 

 situated just anterior to the opening of the common cardinal vein. Probe into 

 the opening and note that the vein comes from the floor of the mouth and pha- 

 ryngeal cavities where it runs alongside the ventral ends of the gill arches. By 

 turning back the flap, previously formed, of the floor of the mouth and pharyngeal 

 cavities, the course of the vein will be more readily followed. Now look into 

 the posterior part of the wall of the sinus, putting this on a stretch. In the 

 median line of the posterior wall will be noted a white fold, and on each side of 

 this is an opening. Probe into both openings and note that your probe passes 

 internal to the coronary ligament and into the liver. Follow your probe into 

 the liver by slitting the substance of the liver, and note the cavity in the right 

 and left lobes of the liver thus revealed. These cavities which extend nearly the 

 entire length of the liver lobes are the hepatic sinuses. 1 The two hepatic sinuses 

 are the persistent proximal parts of the vitelline veins of the embryo. 



Now probe posteriorly into one of the common cardinal veins. Raise the 

 viscera in the anterior part of the pleuroperitoneal cavity and observe that your 

 probe has entered a large bluish sac located in the dorsolateral wall of the pleuro- 

 peritoneal cavity. Follow this sac and its fellow of the opposite side posteriorly. 

 Each bends toward the median region, narrowing considerably, and on pressing 

 the viscera to one side, each may be traced posteriorly as a narrow tube lying 

 immediately to each side of the attachment of the dorsal mesentery to the 

 median dorsal line. These two vessels are the posterior cardinal sinuses; they 

 are the chief somatic veins of the trunk. At the level of the anterior part of 

 the liver the two posterior cardinal sinuses communicate with each other by a 

 broad connection which may be found by probing into the left vein and directing 

 the probe toward the right one. In this same region each vein has on its ventral 

 surface an extensive communication with a large blood sinus, the genital "sinus, 

 surrounding each gonad. Each posterior cardinal sinus also receives numerous 

 segmentally arranged branches from the body wall (parietal veins) and from the 

 kidneys (renal veins). The kidneys are the long, slender, flat organs, brownish 

 in color, which lie immediately lateral to the posterior cardinal sinuses, extend- 

 ing the entire length of the pleuroperitoneal cavity. The parietal and renal veins 

 are readily identifiable in those specimens in which they happen to be filled with 

 blood, but are impossible to see when empty. 



1 Owing to the fact that the veins of elasmobranchs are not definite vessels but spaces in the tissues 

 without definite walls, they are more correctly designated sinuses. 



