DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
35 
The snout is turned downwards, so that its lower angle projects but little beyond 
its upper; from that angle the scooped recurrent cartilages ( l.s.c ., read rc.c.) are seen 
to arise. The highest part of the partition—the crista galli ( cr.g .)—is nearly mid-way 
between the bottom of the sella turcica ( b.s.) and the projecting end of the snout. 
From the septum, in front of that crest, the nasal roof has been cut away ; behind, 
for some distance, the cribriform plate ( cr.p.) grew from the sloping crest near- its 
top. The lowering median cartilage becomes presphenoidal ; it is quite unossified at 
present; the basisphenoid (b.s.) and the basioccipital ( b.o.) are seen, in section, with 
the lowish, thick postclinoid wall between them ; the former is twice as thick and 
half as long as the latter. The large side-wall of cartilage reaching from the nasal 
capsule to the supraoccipital roof (o.s., s.a.c.) has lessened since the first stage (Plate 2, 
fig. 1) to one-half its relative size. Yet the band, even over the protruding alisphenoid, 
is still of considerable thickness. The fore corner of the orbitosphenoid is becom¬ 
ing free, outside the cribriform plate; its main part is only ossified in the narrow 
stem below ; the upper outline is sinuous. The fontanelle between the frontals and 
parietals (f, p.) is nearly filled in by these bones, and the retreating cartilage 
exposes the squamosal ( sq .) somewhat, at the base of the coronal suture. The ali¬ 
sphenoid (above b.s.) is now a single bone, and the foramen ovale (V 3 .) is finished by 
bony growths behind. 
The supratemporal cartilage (s.a.c.) is still two-thirds the width of the tilted 
auditory capsule, which is continuous with the band for some distance, hiding the fore 
part of the great sinus canal (s.c.). Below, and in front of that canal, the elevation for 
the anterior and posterior semicircular canals (a.s.c., p.s.c.) is not great, and the 
hollow for the “flocculus” is shallow. There is a difference of size in the whole 
capsule, and especially in the cochlea, as compared with what we have just seen in an 
embryo of T. hybrida of the same size (fig. 1), that is very remarkable. This species 
also either has a smaller embryo, or its bones develop much earlier than in the other. 
The whole capsule has a well defined, definite outline, often widened into a chink, 
marking it out from the rest of the endocranium. There is a large porch over the 
actual openings of the meatus internus (VII., VIII.); and in front of these the cochlea 
swells up into the cavity of the skull. The occipital cincture is narrower than 
the oblique capsule, and has a very large keystone piece, the supraoccipital ( s.o.). 
The exoccipital ( e.o.) is nearly twice the depth of each interspace of cartilage; it is 
notched for the hypoglossal (XII.), and has a concave face against the emerging vagus 
and glossopharyngeal (X., IX.). 
Besides the large frontal and parietal (f, p.), and the angle of the squamosal 
(sq.), the nasal (n.), the palatine plate of the maxillary and palatine, and the small 
pterygoid (mx., pa., pg.) are all seen edgewise. In this section, detached from the 
skull, the lower jaw and its related parts are shown from the inside ; it has the 
same elegant shape as the other species ; its processes are still cartilaginous at their 
extremities. Meckel’s cartilage (ink), fused with its fellow, is still complete along 
f 2 
