DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
173 
and also tlie squamosals (sq.), are very similar to those of the last kind; there is a 
small club-shaped septo-maxillary (fig. 6, s.mx .) on each side under the second upper 
labial ( u.l h). The parasphenoid (fig. 7, pa.s.) is altogether more slender and pointed 
than that of H. Ewingii, especially in its basi-temporal spurs. The vomers (fig. 7, v.) 
are large; they have a curiously-arched form, a dentigerous lobe twice as large as in 
the last, and come nearer together. The postero-external edge of the bone embraces 
half of the great inner nostril, and the outer spike in front of this passage is but the 
hinder of a series of tooth-like projections of the bone. 
The difference between this skull and that of the “ norma ” is much the same as in 
the last; it comes nearer, however, to the pattern-form, in having the ex-occipitals and 
prootics somewhat marked out, and in having the lateral masses of bone distinct; also 
in having septo-maxillaries. It diverges further in one thing, namely, in having a 
basi-branchial rudiment projecting beyond the basal plate. Both the annulus and 
columella, in these two kinds, come equally short of that which is typical. Here, also, 
we have the optic fenestra and the superobital, both twice as large as in II. Ewingii. 
On the whole, there are about the same number of points in this and the last, in 
which these typical Hglce disagree with the “norma.” 
47. Hyla arborea. —Adult male ; 1-g- inch long. South Europe. 
This is a semi-oval skull, still shorter and broader than the last; the breadth is to 
the length as 6 to 5. 
On the whole, this specimen comes very near to II. Ewingii, notwithstanding the 
distance between the homes of the two species. 
The skull is not quite so depressed as in the two last, and is rougher and stronger 
in its general build ; also it is more fully roofed in. 
The occipital condyles (Plate 32, figs. 1 and 2, oc.c.) are larger and wider apart; 
they are postero-inferior, as in H. Ewingii. 
As in that species, the occipito-otic ossifications are fused together, but in this kind 
there is a basioccipital tract of cartilage (fig. 2, b.o.). 
The canals are larger, but the parotics are similar in both ; there is veiy little 
unossified cartilage near the fenestra ovalis in this species; altogether the ossification 
is more intense above than below; the bone encircles the foramen ovale (V.). 
The three regions of the skull are nearly equal; the single fontanelle ( fo.) is exactly 
one-third the length from snout to occipital condyles; it is an irregular oval, for the 
edges of the tegmen cranii are sinuous. 
The short, wide, depressed mid skull lessens a little from the temples, and enlarges 
again into the superorbital lobes, which are ossified, proximally, by the girdle-bone 
( s.ob., eth.), and are semi-oval, not projecting much more than in II. Ewingii . 
The girdle-bone scarcely occupies a third of the mid skull; and the large optic 
fenestra (II.), which is intermediate in size between that of the two last, is well 
margined with cartilage. 
