Sheet 18.

Figure 1. The Dog-Fish Brain, dorsal view.
Figure 2. Median section of the same. To the right a
more diagrammatic figure. The nerves are numbered:--
[BR1, BR2, BR3, BR4 branches of X forking over the
second to the fifth gillslit.]
cb., cerebellum.
h.s.c., horizontal semi-circular canal of ear, exposed by
the slicing down of the otic mass.
[LAT., lateral-line branch of X.]
m.o., medulla oblongata.
oph., ophthalmic nerve (V.1+VII.1).
op.l., optic lobe.
pit., pituitary body.
pr.c., prosencephalon (cerebral hemisphere).
rh., olfactory lobe (rhinencephalon).
r.t., -its- restiform tracts [of medulla].
-st-. [S.P.G.], stalk of the pineal gland.
th., thalamencephalon.
th.c., thalamencephalon.
-ut., the utriculus, seen through the semi-transparent cartilage-.
Vid., the Vidian branch of VII.
[Visc., visceral branch of X.]
Figure 3. Diagram of the ear of a fish.
The structure of this is easily made out by clearing otic
capsule and cutting slices of the cartilage in the Dog-Fish
(e.g., Figure 1, h.s.c.).
amp., their ampullae.
a.v.c., p.v.c., h.c., anterior, posterior, horizontal canal respectively.
[amp., the ampullae.]
d.e., the ductus endo-lymphaticus.
-sac., the sacculus; c., a small outgrowth of the latter, corresponding
to the rabbit's cochlea-.
-ut., the utriculus-.
Figure 4. The cranium and branchial bars of a Dog-Fish.
The groove in the otic capsule connects the orbital and anterior
cardinal sinuses.
A.C.S., position of the anterior cardinal sinus (dotted outline).
c., the vertebral centra.
c.b., the cerato-branchial.
c.h., the cerato-hyal.
e.b., epi-branchial.
ex.b., extra-branchial.
h.M., the hyo-mandibular.
i.n.p., inter-neural plate.
M.C., Meckel's (lower jaw) bar.
Na.C., the nasal capsule.
n.p., neural plate.
n.s., neural spine.
Ot.C., the otic capsule.
ph.b., the pharyngo-branchial.
P.pt., the palato-pterygoid bar (upper jaw bar).
p.s., pre-spiracular ligament, containing a cartilaginous nodule.
r., rib.
sp., the position of the spiracle.
Figure 5. Diagrams of a vertebral centrum.-- For reference
letters, see text ([Section 9]).
{No Figure 6, in First Edition.}
[Figure 6. Diagram for comparison with Figure III., [Sheet 9].]

Sheet 19.

Figure 1. Amphioxus, seen from the right side. a----b shows the
natural size. The animal is supposed to be clarified, and mounted in
some highly refracting medium, so that it is practically transparent; I.,
II., III., and etc., refer to the section figured on [Sheet 20].
Figure 2. Amphioxus, General Dissection. (Slightly altered from a
figure by Professor E. R. Lankester.) The ventral atrial wall is
removed. The pharynx cut away from the dorsal body-wall, and with
the true ventral body-wall turned over to the (animal's) right. The arrow
a., a., passes through anus to intestine; b., b., is thrust through the
atrial pore to the atrial cavity. Note coe., the body cavity.
References to the two figures.
an., anus.
at., atrial cavity.
at.w., atrial wall.
at.p., atrial pore.
a.d., anterior dilatata of nervous system.
b.w., body-wall.
b.t.L., brown tubes of Lankester.
c.f., ciliated funnel.
coe., coelome.
c.ao., cardiac aorta.
d.ao., dorsal aorta (paired).
d.ao'., dorsal aorta median.
g., gonads (male or female genital gland).
hep., hepatic vein.
in., intestine.
i.w., intestine wall.
lv., liver.
m.f., median fin.
n.c., notochord.
p.v., portal vein.
ph., pharynx.
-p.s.-, [e.s.] pigment spot ("eye spot").
s.c., spinal cord.