DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 25 
third branch of the trigeminal. On the inside the capsule and basioccipital cartilage 
are largely confluent at this part, but this is only for a short distance, between the 
ingoing of the internal carotid and the outgoing of the 9th and 10th nerves. The 
huge, swelling cochlea (see Plate 2, fig. 6, ch/.) causes part of the floor of the capsule 
to appear, in this section, to be seen below the junction of the capsule with the base. 
Outside this part the fenestra rotunda (fr.) is cut across, and then, above it, the 
fenestra ovalis (/%.0.), plugged with the base of the stapes which is cut through, so as 
to show the stapedial artery (sf.a.) in its hole. Here the incus (7.) is severed through 
its body and long crus, so as to show it entire. The annulus and a large part of the 
meatus (i.c.e.) are seen here as cartilaginous bands. The tympanic cavity (c.ty.) is 
lessening. (This section is in front of the last two (figs. 9 and 10) for the supra-auditory 
cartilage (s.a.c.) is separate from the capsule; it should have been described before 
them). 
24th Section (Plate 4, fig. 12).—Here we are behind the cavum tympani, in the 
hinder part of the junction of the capsule with the basioccipital, for the 9th and 10th 
nerves are here cut through (but not lettered). Under the ascending cartilaginous 
wall, where the cartilage has thickened into the wall of the capsule, the anterior sem1- 
circular canal (@.s.c.) is cut across, 
A large, irregular, open space is seen, the vestibule (v).), and in the wall behind it, 
on the outside and below, the facial nerve (VII.) is seen emerging behind the epilyal, 
which is seen here in its union with the capsule. The front face of this section has 
been drawn ; the small recess, here, is the back of the tympanic cavity, and the inser- 
tion of the stapedius muscle is seen below the hole for the escaping facial nerve (VIL). 
Part of the meatus externus (7.a.e.) is laid open, and in the wall of that tube one 
of the imperfect rings of cartilage is shown. The parietal (p.) and the squamosal 
(sq.) are cut through laterally, and, below, the fore edge of the atlas (vt.) comes imto 
view, where it is overlapping the basis-cranii. 
25th Section (Plate 4, fig. 13).—This section is somewhat oblique, both laterally and 
vertically. The mid and hind brain are cut through; the razor has passed close 
behind the basioccipital below, and in front of the supraoccipital above ; hence the 
chondrocranium appears as two distinct tracts, right and left. 
The supra-auditory cartilage (s.a.c.) is very deep here, and below its thick base 
we see the arch of the anterior canal (a.s.c.). This canal is also seen on the inner side 
of the capsule where it joins the posterior canal to form the common sinus ; on the left 
side the horizontal canal (h.s.c.) is also cut across, and below it the ampulla of the 
posterior canal (p.s.c.; see also Plate 2, fig. 1). The foramen for the two larger post- 
auditory nerves shows part of the glosso pharyngeal (IX.), and of the vagus (X.) 
in situ, and that for the hypoglossal (XII.) does the same; the meatus-cartilage 
is cut across. : 
In my first Paper on the Mammalian skull—that of the Pig (Phil. Trans., 1874, 
Plates 28-37), the lateral internal view of the chondrocranium of the 3rd Stage 
MDCCCLXXXV. EK 
