er side, four arterial
trunks, the first of which forks, so that altogether there are five
afferent branchials (a.br.) taking blood to be aerated in the gills, here
highly vascular filamentary outgrowths of the internal walls of the gill
slits.

{Lines from Second Edition only.}
[There are altogether nine vascular outgrowths (demi-branchs), one
on each wall of each gill slit except the last, on the hind wall of
which there is none. (In the spiracle is a miniature demibranch, the
pseudo-branch. This suggests that the spiracle is really a somewhat
modified gill slit.)]

Four efferent branchials (e.br.) carry the aerated blood on to the
dorsal aorta (d.ao.). A carotid artery runs forward to the head, and a
hypo-branchial artery supplies the ventral side of the pharyngeal
region. There are sub-clavian, coeliac, mesenteric, and pelvic
arteries, and the dorsal aorta is continued through the length of the
tail as the caudal artery (Cd.A.).

Section 7. A caudal vein (Cd.V.), bringing blood back from the tail,
splits behind the kidneys (K.), and forms the paired renal portal
veins (r.p.v.), breaking up into a capillary system in the renal organ. A
portal vein brings blood from the intestines to the liver.

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