DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
103 
The wide temporal regions become concave in passing into the orbital, and then the 
skull narrows gently and bulges a little in front, near the ethmo-palantine “ axils.” 
The ethmoidal region (eth.) is covered by a very short “anterior tegmenthe 
margin of this part has a large evenly rounded edge, and so also, in the other 
direction, has the “posterior tegmen,” which is limited to the superoccipital region, 
and is barely twice the breadth of the narrow ledge in front. These two opposite 
margins of the great single fontanelle (Jo.) are very far apart; the hinder is nearly as 
far back as the middle of the auditory capsules; the fore edge is nearly as far forwards 
as the arcuate eth mo-palatine (fig. 1 , pa.). 
The fontanelle, open over three-fourths of the cranial “ barge,” narrows in the 
temporal region, and only recovers three-fourths of its size behind; the roof-bones 
(fp.) are at a considerable distance from it in every part. 
The cartilage which bounds it laterally is narrow in front and widens in the 
temporal region to thrice its first breadth ; this is the lateral remnant of the tegmen 
cranii, and it is, for the most part, quite independent of the walls (see fig. 2), which 
from a little behind the ethmoidal “axils” to the back of the optic foramina (II.) are 
entirely membranous. Thus the optic fenestra (the “ foramen ” is a hole through it) 
is excessively large; a good series of gradations in this respect are to be seen in the 
Australian Anura, and will be described in due time. 
The floor of the skull is very narrow—only half the width of the roof—and is merely 
composed of the trabeculae and an “ intertrabecular ” band of the same width. The 
nasal regions are cpiite normal, except that the subnasal angle is simpler than in the 
type. There is no “rostrum,” and the pro-rhinals ( p.rh .) turn inwards, and are not 
much dilated distally. The roof (fig. 1), widest behind, and the floor, widest in front, 
are normal; the septum ( s.n .) is thick and clearly seen. 
The ossification of this little semi-membranous skull is of great interest, for its 
very minuteness has enabled it to escape from the strict morphological bonds that 
keep the larger kinds in order. 
Nearly all the ossification of the endocranium is behind the orbits ; there are more, 
and there are feioer, osseous centres than in the typical kinds. The additional centres 
are the median bones that have been crushed out, so to speak, by the special law of 
Batrachian morphology ; these have crept in again. 
Fewer centres are seen in the lateral parts, for the occipito-otic centres (prootic and 
ex-occipital, pr.o., e.o.) are here, as in Pseudis and other generalised types, ossified fore 
and aft, without the transverse dividing band of cartilage, seen in those in which the bone 
begins only at the proper nerve outlets. And they are intensely ossified too; only a 
trifling edge of cartilage is left in the tegmen and in the floor (figs. 1 and 2), and in front 
the bony matter takes up half the “ alisphenoidal ” tract, giving a good bony margin to 
the “ foramen ovale ” (V.). The upper and lower median synchondroses are of moderate 
width ; the lower is oblong, and is less than a third the width of the inter-condylar 
