DEVELOPMENT OF THE SKULL IN' THE BATRACHIA. 
189 
cartilages are of full size at present. Besides tire odd outer bone below, two pairs 
more are now present above, and the post- and pre-auditory endoskeletal centres have 
appeared (pa.s.,f.p., px., e.o., and the patch behind V.); three pairs of new cartilages, 
also, have appeared—the spiracular and the permanent upper labials ( sp.c., u.P.u.l 2 .). 
The notochord (no.) is fast shrinking ; the condyles ( oc.c.) are well formed ; and a 
crescentic bony tract appears on each side, reaching to the foramen for the 9th and 
10th nerves (IX., X.) ; these are the ex-occipitals (e.o.) ; they are climbing up behind, 
and flanking the auditory capsules in the opisthotic region ; the prootics are small. 
The whole basis cranii is now well chondrified, and behind, has completely coalesced with 
the auditory capsules; they are oblicpiely placed, the horizontal canal ( h.s.c .) and its 
fringing tegmen ( t.ty.) pushing outwards. Outside the oblique, oval, vestibular con¬ 
vexity, below, we see a perfect oval stapes (fig. 11, vb., st.) ; and between the otic process 
of the suspensorium (otp.) and the capsule there is a thick biconvex mass of cartilage 
wedged in ; this is the distinct spiracular cartilage (sp.c.) —the “annulus tympanicus” 
that is to be. The interorbital region, or mid skull, lessens considerably forwards, and 
bulges gently ; its floor is perfect and so are its walls, but the roof is membranous from 
the narrow occipital arch (lettered f.m.) to the perpendicular ethmoid (the hind part of 
s.n.) : this is the great fontanelle ( fo.). The rudiment of an ethmo-nasal wall seen in 
the last stage (fig. 8, p.e.) is now complete, and yet has quite a clear outline above and 
below (figs. 10, 11, s.n.) ; this is the high fore part of the intertrabecula, which often, 
in this “Family” (the Hylidee), grows forwards as a free prenasal rostrum. The broad 
bulbous hinder end is directly in front of the parasphenoid below, and of the fontanelle 
above ; its fore end is narrow and is still growing, for it will run forwards between, and 
even in front of, the cornua trabeculae (c.tr.). Here we see the distinction between the 
nasal roof-cartilage ( n.r .), or ali-septals, and that growth of the skull itself at its closing 
in, which belongs to the true ethmoidal region. Here the hind part of the roof is the 
ali-etlunoid (al.e.) —an ox-liorn-shaped spreading and curving growth of cartilaginous 
wings, enfolding the sides and hind part of the nasal sacs. The nasal roofs (n.r.) 
are broad lunules of newer cartilage, their deep concavity, or notch, margining the 
nostrils (e.n.). 
The cornua trabeculae (c.tr.) are quite like those of the last stage (figs. 8 and 9), but 
they have dwindled down to half their proper size. In front of these, but more than 
twice as large, are the temporary upper labials (u.l.); these have a deep cleft behind, 
more than half dividing each, and a long round outer angle ; the outer part corresponds 
to the angulo-labial of the Lamprey, and the inner moiety to half its anterior dorsal 
cartilage, or main upper labial. 
Behind this inner part, running obliquely backwards and outwards, there is a half¬ 
tube of thin bone, rather dilated at its base, in front ; this is the premaxillary (px.), 
which thus develops its nasal process, first. 
Each bone reaches the front of the outer nostril (e.n.), and bas under it two little 
beads of new cartilage ; the inner lobule lies under the bone and is discoid; the 
