Section 8. Instead of Being Tubular Vessels, the Chief Veins of the

dog-fish are, in many cases, irregular baggy sinuses. Three main venous trunks flow into the sinus venosus. In the median line from behind comes the hepatic sinus (H.S.); and laterally, from a dorsal direction, the Cuvierian sinuses (C.S.) enter it. These, as the student will presently perceive, are the equivalents of the rabbit's superior cavae. They receive, near their confluence with the sinus venosus, the inferior jugular vein (I.J.V.). At their dorsal origin, they are formed by the meeting of the anterior (A.C.S.) and posterior (P.C.S.) cardinal sinuses. The anterior cardinal sinus -is, roughly, the equivalent of the internal jugular vein-, lies along dorsal to the gill slits (g.s.), and receives an orbital sinus from the eye. The posterior cardinal sinus receives a sub-clavian vein (s.c.v.) and a lateral vein (L.V.), and fuses posteriorly with its fellow in the middle line. This median fusion is a departure from the normal fish type. It must not be confused with the inferior cava, which is not found in the dog-fish, the [right] posterior cardinals representing the rabbit's azygos vein. A simplified diagram of the circulation of a fish is given in Figure 2, Sheet 16, and this should be carefully compared with the corresponding small figure given of the vascular system of our other types.

{Lines from Second Edition only.} [The blood of the dog-fish resembles that of the frog.]