DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
261 
fig. 4, sq.), close to the large air cavities within, is also well seen. The interparietal 
li.p.) has begun to develop the occipital crest so large in the adult (Plate 39, fig. 4). 
Stages 2 and 3 (b and c).— Showing endocranium and certain of the investing 
hones of Galeopithecus philippensis. 
These two stages differ but little from each other, and for the advance of the endo¬ 
cranium may be taken together. In the longitudinally vertical section (Plate 38, 
fig. 7) the cranial cavity, and the nasal labyrinth are equal in length ; the former 
overlaps the latter in front. The obliquity of the top of the perpendicular ethmoid 
(p.e.) is such as to make a very obtuse angle with the top of the general septum 
(p.e., s.n.), whilst it is almost in a line with the basis cranii behind, just rising a 
little at the crista galli ( cr.g .). The recess for the olfactory lobe, lying on the 
oblique cribriform plate, is not large—very little in advance of the same in the 
Marsupials. Only about a fifth of the general partition ( p.e .) is ossified at present; 
this is a long wmy from the presphenoid ( p.s .) and does not reach the bottom ; the 
intertrabecula itself is hardly touched, only its crest. 
This is a very long septum (p.e., s.n.) for so short a snout; in most of the Insecti- 
vora it is that part wdiich prolongs the septum, forwards ; here, it is the elongated 
facial region itself, with but little alinasal addition. The deflection of the whole face 
is still evident, and the end of the septum is almost in a line with the general palatal 
tract. Behind that part the opening of Jacobson’s organ (j.o.) and the fore part of 
its cartilaginous capsule of the near side is shown; behind, where it is cut across, the 
vomer (v.) is seen. 
That long trough of bone is half the length of the cranio-facial base, reaching from 
the front third of Jacobson’s (recurrent) cartilage (rc.c.) to behind the middle of the 
presphenoid (p.s.). As it supports the intertrabecular base of the nasal partition, so 
it is itself supported by the bones of the hard palate ( p.mx., pa.) at their junction 
along the mid-line; thus the nasal cavities as they pass towards this hinder opening 
are kept distinct. 
Over the septum nasi (s.n.) the nasal (n.) is seen, and the frontal (f.) over the 
ethmoid, and over the cavity of the skul] in front. At this stage the roof-bones are 
thick; the parietal receives the hinder angle of the frontal into a notch, laterally, 
and is partly overlapped by, and partly overlaps, the frontal. The well-ossified 
anterior sphenoid (o.s., p.s.) is seen in this view, the wing rising into a rounded angle, 
and having the large optic foramen (II.) near its hind edge below; the presphenoidal 
tract is rather thick, and is longer than the bony plate—basisphenoid (b.s.) —behind 
it. The alisphenoid (al.s.) leans against the orbitosphenoid, and rises to the same 
height; it overlaps it in front, and is then only partially visible in this view. 
The short basisphenoid (b.s.) dips a little, but gets no postclinoid ridge again, behind; 
there is a small tract of cartilage between all these basal bones (p.s., b.s., b.o.). Under 
