THE PERCH 51 



from the false diaphragm and find it. Joining each end of the trans- 

 verse sinus venosus is a large and conspicuous duct, or sinus, called 

 the Cuvierian duct. The two Cuvierian ducts lie along the anterior 

 end of the abdominal cavity, parallel with each other and just in 

 front of the liver, between the sinus venosus and the head kidney. 

 Inasmuch as the head kidney is dorsal in position, and the sinus 

 venosus ventral, the Cuvierian ducts have an almost vertical posi- 

 tion in the body. Trace these vessels from the sinus venosus dor- 

 sally ; they will be found just behind the posterior gill arch. The 

 dorsal ends of these two ducts are connected by a horizontal sinus 

 which lies just beneath the spinal column. 



Two pairs of prominent veins— the jugulars or anterior cardi- 

 nals, and the posterior cardinals— bring blood from the anterior 

 and the posterior portions of the body, respectively, to the horizon- 

 tal sinus of the Cuvierian ducts. Just before joining the sinus the 

 two jugulars unite and form a median vein; the two posterior 

 cardinals also unite and form a median vein. 



The two posterior cardinals are large and prominent veins and 

 lie just beneath the vertebral column, partly embedded in the kid- 

 neys; the dorsal aorta lies between them. The left cardinal is 

 much larger than the right, and much longer, and begins its course 

 at the posterior end of the body as the caudal. vein; this vein lies 

 in the ventral arches of the spinal column and receives the paired 

 spinal veins. 



In the trunk region it receives the left spinal and renal veins. 

 The right cardinal begins its course in the hinder part of the body 

 cavity and receives the right spinal and renal veins. Find the 

 cardinals in the mass of the kidneys and trace them forward to 

 the median cardinal and the Cuvierian ducts. 



Find the median jugular vein, and^ trace it and the two jugulars 

 and their branches as far as possible. 



Entering the horizontal sinus are three additional veins. Two 

 of these are the small paired subclavian veins, which bring blood 

 from the pectoral fins ; the third is the intestinal vein, which brings 

 blood from the stomach, intestine, and genital organs. Follow the 

 course of these veins and their branches. 

 Exercise 21. Draw a diagram of the venous system, so far as observed. 



