The arteries carrying blood from the ventral aorta to the gills are named the _afferent branchial arteries_. Observe the relation of these vessels to the gills.
VENOUS SYSTEM. All the blood of the body is conveyed to the sinus venosus. The sides of the sinus venosus are extended as large vessels, already referred to as the ducti cuvierii. Open the sinus and ducti by a transverse ventral incision. The ducti pass directly into the lateral veins. Near the middle of the posterior wall of the sinus is an aperture of varying size, the opening of the _hepatic sinus_; there are rarely two openings in Squalus, always two in Eugaleus. A large opening on the posterior wall of each ductus leads into the _posterior cardinal vein_. On the anterior wall of the ductus, near the sinus venosus, is a small aperture, that of the _inferior jugular vein_. Lateral to this is frequently a somewhat larger opening of the _anterior cardinal vein_. This is absent, however, in the majority of specimens; the anterior cardinals opening into the anterior ends of the posterior cardinals in about six out of ten cases.
A large cavity, the _hepatic sinus_, exists in the anterior end of the liver just posterior to the suspensory ligament. Cut into the liver at this point until the sinus is found, open it, and observe the large _hepatic veins_ bringing blood into it from the liver, as well as its communication with the sinus venosus.
Trace all veins by passing a flexible probe or guarded bristle along them and then opening the vein with the probe as a guide. All smaller vessels emptying into those described should be noted.
The _lateral veins_ pass forward to the posterior edge of the pectoral girdle, bend sharply dorsad, and enter the lateral extremities of the ducti cuvierii. Open a lateral vein near the anterior end and trace it toward the heart. The right and left lateral veins are joined by a vein passing along the ventral bar of the pectoral girdle. Open the lateral veins at a point about two inches in front of the pelvic girdle and trace the veins backward as far as they can be followed. The blood from the pelvic fins enters the lateral vein through the _femoral vein_. The lateral veins finally unite back of the cloaca.