A MANUAL OF ZOOLOGY , 39 



dorsal aorta. The one arising from the posterior gill- 

 cleft unites with the one in front of it. Open the spiracle 

 and see if you can demonstrate that it is a rudimentary 

 gill-cleft. From the first or anterior pair of efferent bran- 

 chial arteries trace forward the two common carotid arter- 

 ies. Note that each one of these divides into two 

 branches; an external which goes to the eye and surround- 

 ing region, an internal which, approaching its mate from 

 the opposite side, pierces through on the median line and 

 supplies the brain. Trace the dorsal aorta posteriorly. 

 Note and trace the first branches, the two subclavian ar- 

 teries to the pectoral fins. Posterior to the subclavian 

 arteries the first median or coeliac axis is given off. 



Trace this through its iflrst branch, the anterior gas- 

 tric, to the front part of the stomach, and through its 

 second branch, the hepatic, to the liver. The second 

 median artery, the anterior mesenteric sends a branch, 

 the lineo-gastric, to, the posterior part of the stomach and 

 another to the spleen. Demonstrate this. The third 

 median artery, th€> posterior mesenteric, supplies tlie rec- 

 tum and the rectal glands. Trace these points oiit. The 

 dorsal aorta also gives branches to the genital organs, 

 the kidneys, and the pelvic fins. It continues into the 

 tail as the caudal artery. 



The venous system can be traced from the sinus 

 venosus by three veins which lead into it. A pair of 

 smaller ones, the hepatic veins, come from the liver. The 

 larger, a short trunk directed anteriorly and ventrally, 

 the pectoral sinus or ductus Cuvieri, receives the subcla- 

 vian veins. The ductus Cuvieri is formed by a pair of 

 jugular or anterior catidinal vems returning the blood from 

 the head region, and a pair of posterior cardinals bringing 

 the blood from the posterior regions. Bach anterior cardinal 

 has an expansion, the orbital sinus, which surrounds the 

 eye. The veins entering the kidneys from the tail are 

 often called caudal veins, but may be considered as the 

 posterior cardinals which, after performing the portal cir- 

 culation of the kidneys, collect and empty into the ductus 

 Cuvieri. The hepatic portal vein is formed by the junction 

 of veins from the intestines, pancreas, and the spleen. 

 The lateral vein brings blood from the femoral and some 



