DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
79 
Thus in a side view (fig. 4) the wall is about half of it bony, but this is due to the 
curling over of the roof; the “ sphenethmoidal ” wall itself is quite unossified. The 
orbito-sphenoidal region is largely fenestrate ( o.s.f'.), as in Lizards, but in a very different 
* manner. 
In this stage the fontanelle (fig. 2 ,fo.) is seen in front between the diverging ends 
of the frontals, and behind, as a lozenge-shaped space (/o'.) between the frontals and 
parietals. 
Laterally, the ear-capsules are very large relatively (compare Plate 11, figs. 1-3; 
and Plate 12, figs. 2-4) ; and the tegmen tympani with the enclosed horizontal canal 
(t.ty.) projects much in front; this part is not ossified. 
Below (fig. 3), the two unossified vestibules, embraced at their inner margin b}^ the 
large grooved ex-occipitals, resemble a pair of symmetrically imbedded acorns, the 
rough “cup” being bony, and the smooth “fruit” cartilaginous. 
Each of these capsules is fenestrate, and operculate, obliquely; the opercular stapes 
(, st .) looking outwards and somewhat backwards; the rough “cup” is perforated in 
two places for the glosso-pharyngeal and vagus nerves (IX., X.). In front, the bony 
matter scarcely reaches the 5th nerve (V.); the optic nerve (II.) passes out of the hind 
part of the orbito-sphenoidal fenestra, and the olfactory escapes through the closing 
wall in front. 
The fore part of the tegmen cranii is rather long; laterally, it is articulated to 
the ethmo-palatine [e.pa.) ; in front, it passes into the two narrow crescentic nasal 
roofs (fig. 4, al.sp.), which are partly covered by the small ear-shaped nasal bones (n.). 
The nasal floor (fig. 3, s.n.l.) is of the normal breadth, and in front it is now a finished 
structure, elegantly crenate, with seven lobes. 
The outer of these are the outer angles of the trabecular cornua, now finishing the 
nasal floor in front. Next to these, but on a higher plane, are the horns of the nasal 
crescents (s.n., al.sp.). Near the mid-line we see a pair of short inturned pointed 
“ pro-rhinals ” (p.rh.) ; and now, at the middle, there is a little bud of cartilage, the 
prenasal ( p.n.). 
Besides the nasal roof-bones ( n .), there are now, below, two oval dentigerous plates, 
placed transversely and some distance apart; they touch the inner nostril (i.n.) by their 
outer edge ; these are the vomers (y.). 
The semi-oval outline of the face is now nearly finished by the dentigerous pre- 
maxillaries and maxillaries (fig. 4, px., mx.) ; most of the maxillary bone is moulded 
on a cartilaginous bar, which is quite unlike anything seen in the last stage. 
The solid ethmo-palatine bar (Plate 11, fig. 1 ; and Plate 12, fig. 1, pt.pa.) is now 
(Plate 12, fig. 4, e.pa., pt.pa.) a slender rod, flatter below than above, and instead of 
being curved forwards outside, it is turned suddenly backwards. 
The prepalatine spike (fig. 3 , pr.pa.), which turned directly inwards in the second 
stage and touched the trabecula (Plate 11, figs. 1-3) now has its outer margin coincident 
