74 
MR. W. K. PARKER OK THE STRUCTURE AKD 
very much shrunken. The wiki and general growth of bony matter, without division 
into periotic and occipital regions, is now still more remarkable, and, above, the right 
and left tracts are rapidly coalescing, so that there is no superoccipital cartilage 
(Plate 11, fig. 1). This bony matter reaches forwards to the great fontanelle {fo.) and 
laterally up to the inner margin of the horizontal canal (inside t.ty.). 
Below (fig. 2) there is a wide basioccipital tract [iv.) unossified, and the bony 
matter only skirts the floor of the vestibule ; it runs, however, well round the pre- and 
post-auditory nerve-passages (V., IX., X.). 
The steeply-sloping floor of the tympanic cavity (Plate 11, fig. 3 ,fty.) has become 
much reduced in size, and thus the oval stapes (st.) is seen clearly from below. 
The fontanelle (fo. ) has the same relative size, and so have the fronto-parietal bones 
( f.p .) ; but the upper part of the skull in the ethmoidal region has altered greatly; 
ready to alter still more as the tail, and indeed the whole creature, keeps lessening 
in size. 
The ethmoidal roof (Plate 11, fig. 1 , p.e.) has grown over the growing septum nasi, 
but the nasal roofs are still membranous, or only composed of soft cartilage. 
The back wall of the nasal fossae is not so distinctly articulated to the edge of the 
tegmen cranii; but, gently shelving down, the median part passes into a concavity 
which lies between the roof and the post-palatine ( pt.pa .). The cornua trabeculae 
(c.tr.) have largely united together, but a small hole some distance behind the notch 
may be still seen : this soon fills in, it represents the large open space in the “ Urodeles.” 
The post-palatines (pt.pa.) have been, as it were, moulded into a more solid, but 
altogether a rounder and smoother, structure; the sharp crest has become a neat 
longitudinal ridge, and the hinder process is not a flap but a geniculate projection into 
the fore part of the suborbital fenestra. 
Laterally (Plate 11, fig. 3, pt.pa.), it appears as a gently concave plate, like a “post- 
zygapophysisthe orbitar process playing against its scooped face. The fore part of 
the palatine has chondrified the pre-palatine ligament, and the apex of this bar abuts 
against the trabecular cornu ( pr.pa ., c.tr.) ; thus the internal nostril (i.n.) is fairly 
enclosed by cartilage. 
Beneath (Plate 11, fig. 2), the trabecular, palatine, and suspensorial regions all pass 
gently into each other; this, however, is a very temporary condition. 
Besides the general lessening of the cartilage, the suspensorium is not now so bent 
outwards, and the “ pedicle ’ has bent itself into a sigmoid form for want of room 
(fig. 2 ,pd.). 
The space between the “ elbow ” of the suspensorium and the spiracular cartilage or 
otic process ( ot.p.) is larger, and that band seems to belong equally to the tegmen 
tympani and the suspensorium; the ridged edge of the orbitar process (or.p.) runs 
along to the tegmen, strengthening the whole band ; this “ extra-suspensorial ” tract 
has no counterpart in the Lamprey. 
The quadrate region (q.) stands out further from the trabecular cornu, and its 
