On 
or 
On 
Cuap. II. FOLDINGS OF THE EMBRYONIC DISC. 
numerous (Pl. 17, fig. 6). The vascular area covers more than half of the yolk 
mass, and plunges deeply into its interior (Pl. 15, fig. 11, 12, 12a; Pl. 16, fig. 5). 
The vena afferens plunges suddenly into the mass of the yolk at a point close 
to the head (Pl. 15, fig. 12). The vena terminalis has sunk still further below 
the surface of the yolk, and at the superficial termination of the vascular area 
the vessels become very numerous and anastomose freely with one another and 
with those situated more deeply (Pl. 17, fig. 6). 
The feet (Pl. 14, fig 1; Pl. 15, fig 12; Pl. 16, fig. 5; Pl. 25, fig. 11) begin 
to show signs of the toes, and the tissue (PI. 21, fig. 22, 22a, 24) in such places 
has a different appearance from that of the neighboring parts; but as yet the for- 
mer passes gradually into the latter (Pl. 21, fig. 25.) The form of the feet is 
changed, either to a broader fan-shaped figure, as among the Chelydroide (Pl. 14, 
fig. 1; Pl. 15, fig. 12) and Emydoide, (Pl. 16, fig. 5; Pl. 25, fig. 11,) or to a more 
elongated and oar-shaped form, as among the Chelonioide (PI. 6, fig. 22). The anus 
(Pl. 14, fig. 1) is a very prominent feature at this age, just as it is in the adults 
of some of the lower families, namely, in the Chelonioidee and Trionychide. 
In the next phase, (Pl. 18a, fig. 2; 3; Pl. 17, fig. 2,3, 3a, 7; Pl 18, fig. dns 
Pl, 19, fig. 18,°18a, 18b, 18¢; Pl. 20, fig: 2; Pl. °23, fig, 2, 2a, 2b, 2c, 2d, 2e, 
Of, 20, 2h; Pl. 24, fig. 5; Pl. 25, fig. 4, wood-cut 2,) the former great dispropor- 
tion Piven the head and body has lessened very much, the body having grown 
faster than the head. The embryo has the power to move not only the head 
and feet and tail, and the lower jaw and tongue, but also the toes, separately, 
and to roll the eyes. The shield (Pl. 18a, fig. 2 and 3) has become a very 
prominent feature, and the ribs are quite marked. 
The brain (Pl. 23, fig. 2, 2a, 2b, 2c, 2d) has its different regions more dis- 
Lone marked out; the olfactory lobes, (fig. 2, 2a, 2b, ¢,) and the cerebellum 
(fig. 2, 2a, 2b, e) in particular, are more prominent, and the olfactory nerve more 
lengthened (fig. 2, 2a, 2b, from ¢, to c'). The more elongated hemispheres (fig. 2, 
2a, 2b, @) are nearly on a level with, and more closely approximated to, the cor- 
pora quadrigemina, (fig. 2, 2a, 2b, ,) so as to touch them, and cover at least two 
thirds of the pineal gland (fig. 2a, 2b, d). The communications between the differ- 
ent lobes are narrower, both between those of the same side and those of opposite 
halves. This is especially marked in reference to the opening (fig. 2b, m) between 
the two hemispheres (a). The medulla oblongata (Pl. 23, fig. 2, f, 2a, f, 2b, /) is 
bent forward and downward at an acute angle upon itself, so that the point 
from whence the acoustic nerve (fig. 2, 7) arises, touches the lower border of the 
optic lobe (fig. 2, #). The bloodvessels of the arachnoid plexus, which terminate 
suddenly, (Pl. 23, fig. 2b, g, 2e, 2f, 22, 2h,) have become quite numerous and elon- 
gated. The vascular covering to the fourth ventricle (fig. 2b, y’) is highly dey eloped. 
