636 
Fig. 9. 
EXPLANATION 
fiz. 5; fig. 6a, in alcohol, c, the cell wall has shrunk; fig. 
6b, a single blastematous cavity (a); 0, the cell wall 
shrunk; c, the mesoblast; the same as fig. 5. 
Fig. 7. Part of a longitudinal section through the middle of 
the eye of an adult Trachemys serrata, 10 diam. ; a, scle- 
rotie portion of the conjunctiva; a’, conjunctiva; a’, fold 
where a and a' join; }, sclerotica; c, sclerotic squamula ; 
cl, cornea; c, base of iris; d, pigment layer; e, choroi- 
dea; é', iris; ¢, posterior lining of the iris, or ciliary pro- 
cess; e°, posterior border of the ciliary process; f, /*, 
pigment layer lining the choroidea (¢); g, membrana 
Jacobi; g', anterior border of g; h, retina; ’, anterior 
edge of h; i, fibrous layer; &, membrana hyaloidea; 2’, 
prolongation of & over the back of the crystalline lens 
(1); k, fold where & recurves; /, crystalline lens; m, m’, 
triple wall of the capsule of the lens; n, the membrana 
pupillaris ; n', border of n. 
Fig. 8. Longitudinal section through the middle of the left 
eye of a Turtle just hatched, about 10 diam. The optic 
nerve (h') is introduced here out of place, to show its 
relation to the retina. The letters are the same as in fig. 
7, to which are added: 6", continuation of the sclerotica 
over the optic nerve; d', posterior termination of the 
pigment layer which covers the choroidea (e) ; é*, (this 
letter is erroneously marked e! in the plate, near X’,) 
continuation of the choroidea (¢) over the optic nerve, 
i’; fig. 8a, portion of fig. 8, about 20 diam., to show more 
distinctly the different membranes and layers of the eye 
bulb. The letters are the same as in fig. 8. 
Transverse section of the head through the eyes, 
10 diam., date not noticed; a, musculo-cutaneous layer ; 
b, corpora quadrigemina; ec, eye; c', aqueous humor; c’, 
crystalline lens; d, vitreous humor ; d/, retina; e, anterior 
half of the orbit of the eye, empty; 6', hemispheres; 27, 
the separate edges of b". 
PLATE XXIII. 
[Drawn from nature, by H. J. Clark. | 
All the figures are from Chelydra serpentina. Fig. 1, 1a, 2, 
2a, 2b, 2c, 2d, and 3, are all lettered alike: a, hemi- 
spheres; }, corpora quadrigemina ; ¢, olfactory bulb; c’, 
Schneiderian membrane ; c!!, the same as c! cut across ; 
c!!!, septum marium; d, pineal gland; e, cerebellum; e/, 
edge of the still open portion of the spinal tube ; /, upper 
wall of the spinal tube ; g, vascular pia mater ; g/, choroid 
plexus over the medulla oblongata (p); 4, the eyes; 2, 
spinal tube ; k, optic lobes; x’, optic nerve; /, auditory 
OF 
Fig. 1. 
THE PLATES. 
nerve ; m, opening on the inner face of the hemispheres ; 
n, commissure of the hemispheres ; 9, floor of b, the so- 
called pons Varolii; o', fourth ventricle ; p, medulla ob- 
longata; p!, commissure of the optic lobe ; p!’, anterior 
end of the commissure of the optic lobe. 
View of the left side of the brain and part of the 
spinal tube, about 3 diam. Laid June 23, opened Aug. 
22, 1855; fig. 1a, the same as fig. 1, a longitudinal me- 
dian section ; about 4 diam. 
Fig. 2. Left side of the brain and part of the spinal tube, 
3diam. Laid June 12, opened Aug. 16, 1855. Fig. 2a, 
view from above of fig. 2; 3 diam. From c toc’, the 
olfactory nerve and the Schneiderian membrane are 
raised up higher than is natural. Fig. 2b, longitudinal 
(in 
this figure p should be &, and &, just before it, should be 
kl.) Fig. 2c, transverse section of the Schneiderian 
median section of fig. 2 and 2a; nearly 6 diam. 
membrane; 10 diam. Fig. 2d, longitudinal and horizon- 
tal section of the hemisphere, exposing the interior and 
the corpora striata (7); a, walls of the hemispheres; c, 
olfactory lobe ; ¢!’, olfactory nerve. Fig. 2e, the choroid 
plexus taken out from the hemisphere, 20 diam. Fig. 2f, 
small tuft of fig. 2e. Fig. 2, profile of fig. 2f; s, a single 
vessel from which several are budding. Fig. 2h, end of 
one of these vessels; a, inner wall, formed of long co- 
lumnar cells; }, outer wall, formed of short and broad 
cells; the centre is full of blood corpuscles; 500 diam. 
Fig. 8. Longitudinal section of the brain and the skull, 5 
diam. ; 1, designates the crest of the occipital bone; 2, 
the base of the skull; 3, the ethmoid; 4, the end of the 
skull; 5, the end of the vomer; 6, the sphenoid; 7, the 
vertebre of the neck; 8, the cartilaginous upper max- 
illary ; 9, the entrance to the nostrils. Laid June 12, 
opened Aug. 28, 1855. 
Fig. 4; compare wood-cut 3, p.576. Longitudinal section of 
the head of a Turtle just hatched; 5 diam. An alcoholic 
specimen was used on account of the hardening of the brain ; 
a, entrance to the nasal cavity; b, nasal cavity around 
which the Schneiderian expands; ¢, olfactory nerve; d, 
olfactory lobe; e, hemisphere with an opening on the inner 
face next to the commissure for the passage of the blood- 
vessel, (e/,) which expands in the interior into a vascular 
plexus in the form of a tuft; /, pineal gland, its superior 
or outer commissure (/’) cut through; g, corpus quadri- 
geminum, cut at the commissure so as to allow an interior 
view. The outlines of the surface of the right lobe may 
be seen in the distance under the vascular membrane (g’) ; 
g'', bloodvessel of the enveloping membrane, (pia mater,) 
which plunges between the corpora quadrigemina and 
the cerebellum (4); the same passes backwards into the 

