mouth is rough with denticles, and has a
fleshy immovable tongue on its floor. In the position of the
Eustachian tube there is a passage, the spiracle (sp.), running out to
the exterior just external to the cartilage containing the ear. The
pharynx communicates with the exterior through five gill slits (g.s.),
and has, of course, no glottis or other lung opening. There is a wide
oesophagus passing into a U-shaped stomach (st.), having, like the
rabbit's, the spleen (sp.) on its outer curvature. There is no coiling
small intestine, but the short portion, receiving the bile duct (b.d.)
and duct of the pancreas (pan.), is called the duodenum (d'dum.). The
liver has large left (L.lv.) and right lobes, and a median lobe (M.lv.), in
which the gall bladder (g.bl.) is embedded. The next segment of the
intestine is fusiform, containing a spiral valve (Figure 4), the shelf of
which points steeply forward; it is sometimes called the colon (co.). It
is absorptive in function and probably represents morphologically, as
it does physiologically, the greater portion of the small intestine. A
rectal gland (r.g.) opens from the dorsal side into the final portion of
the canal (rectum).

Section 5. The circulation presents, in many respects, an
approximation to the state of affairs in the developing embryos of the
higher types. The heart (Figure 3, Sheet -14- {Error in First Edition}
[16]) is roughly, Z shape, and transmits only venous blood. It lies in a
cavity, the pericardial cavity (P.c.c.), cut off by a partition from the
general coelome. At one point this partition is imperfect, and the two
spaces communicate through a pericardio-peritoneal canal (p.p.c.),
which is also indicated by an arrow (p.p.) in the position and direction
in which the student, when dissecting, should thrust his "seeker," in
Figure 1 Sheet 15. A sinus venosus (s.v. in Figure 3, Sheet 16)
receives the venous trunks, and carries the blood through a valve into
the baggy and transversely extended -auricle- [atrium] (au.), whence it
passes into the muscular ventricle (Vn.), and thence into the truncus
arteriosus. This truncus consists of two parts: the first, the conus or
pylangium (c.a.), muscular, contractile, and containing a series of
valves; the second, the bulbus or synangium (b.a.), without valves and
pulsatile. In the rabbit both sinus and truncus are absent, or merged in
the adjacent parts of the heart.

Section 6. From the bulbus there branch, on eith