DEVELOPMENT OF THE SKULL IN THE MAMMALTA. toh 
The auditory capsule is largely ossified, especially on this, its inner, face ; the “ crest” 
of cartilage is not quite gone, nor quite ossified. The recess for the flocculus (jl.7.) 
under the arch of the anterior canal (a.s.c.) is about the size of the meatus internus 
or vestibular eave leading to the foramina for the 7th and 8th nerves (VIL, VIIL.). 
The other foramina ([X., X., XII.) in front of, and through, the occipital arch (s.0., 
¢.0., b.0.) are seen in this section. 
Part of the outer view of the hind skull (Plate 19, fig. 9) shows the normal division 
of the petromastoid into prootic, epiotic, and opisthotic centres (pr.o., ep., ep.), but 
the wedge-like epiotic is not a very distinct tract; it is bound to the rest of the 
main centre—the opisthotic—on its inner side. 
There is still unossified cartilaye over the anterior canal, and outside its ampulla, 
and that of the horizontal canal; the paroccipital process (p.oc.) is still cartilaginous, 
and also the stem of the epihyal (e.hy.). 
These parts are also seen in the end view (Plate 19, fig. 6), which displays the 
occipital arch perfectly, and the auditory capsules partially ; the broad cartilaginous 
tracts, here seen, give the whole structure depicted a diagrammatic distinctness. 
In the lower view of this perfect skull (Plate 20, fig. 1) the broad snout in front, and 
the broad basis cranii, behind, are displayed, fore and aft of the large investing bones 
of the upper face and palate, 
The hinder part of the anterior sphenoid (0.s., p.s.) is seen behind the hard palate, 
in the roof of the nasopalatine canal, in the middle, and, right and left, in the wall of 
the orbit. The top of the orbitosphenoid (o.s.) is still unossitied, and the presphenoid 
has been formed by the fusion of the proximal parts of the ossified tracts, right and 
left, of the two orbitosphenoids (see also Plate 19, fig. 8). 
But the posterior sphenoid is freely displayed in this aspect, covered, however, in 
one part, by the small pterygoids ( pg.) that have coalesced with it by their subcranial 
flange. 
The suture, right and left, between the alae and the base (q/,s., b.s.), is fast dis- 
appearing, so that the whole tract which forms so large a part of the base and lower 
wall of the cranium, proper, is now practically one bone. The well-formed temporal 
squama (sq.) forms a slightly squamous suture with the outer edge of the alisphenoid 
(al.s.), which, in turn, lies some distance outside the orbitosphenoid (0.s.). But in 
this view the squamosals are seen only to form a thin clamp to the alisphenoids, which 
stretch across the wide tract that intervenes between the hard palate and the auditory 
capsules. In front of the squamous suture the alisphenoid is notched and uncinate at 
its antero-external angle, and then has a somewhat notched, thick margin bordering 
9 
the sphenoidal fissure (V1, V*.). Behind this fissure the palatine bone is seen to hook 
¢ 
itself round the front and outside of the small, oval, oblique “ external pterygoid 
plate” (epg.). A moderate fossa is seen between this piece of carpentry and the 
ankylosed pterygoid bone ( pg.), behind which a small foramen is seen. The foramen 
ovale (V*.) forms a conspicuous opening, behind, and further outwards, than the 
