DEVELOPMENT OP THE SKULL IN THE BATRACHIA. 
185 
The outline is semi-oval, ancl the length is to the breadth as 10 to 11 ; the hinge 
of the jaw has got no further back than the end of the upper bar of the squamosal 
(sq., q.c.), in this it is in strong contrast with the skull of Hyla alhomarginata. 
The obliquity of the parotic wings is much more evident than it is in that species 
(see Plate 32, figs. 6, 7); a line drawn along the hind margin of the auditory capsule, 
touching the end of the tegmen tympani and the epiotic eminence, would form, 
with a transverse line intersecting it, an angle only half as acute as would be 
obtained by the same measurement in the skull of that species of Hyla; I shall 
take that species for my model of comparison in describing this. In this skull the 
moderate degree of retreat of the jaw-hinge makes the suspensorium form a little 
less than a right angle with the basi-facial line; and there is a great obliquity of the 
squamosal (sq.) outlying it, the hammerlike head of which is tilted downwards to 
articulate with the jugal process of the maxillary. 
Without any loss of elasticity—for soft tracts of cartilage alternate with hard 
territories of bone—this skull is one of the strongest, for its size, of any to be found 
in the “ Orderalbeit, like that of a Crocodile, it retains not only much cartilage, 
but, also, nearly all its sutures. 
We have, here, the normal proportion of the three (serial) regions of the skull; the 
auditory and nasal are about equal, and the orbital one-third larger ; measured across 
the axis, the middle region has its cranial part very large, thus lessening the orbital 
vacuities. 
The occipital condyles (oc.c.) are semi-ovoidal, and are postero-inferior; they are 
separated by a straight basal space one-third larger than their long axis. Over and 
below the large foramen magnum there is a clear cartilaginous supra- and basioccipital 
tract of cartilage (behind f p. and at b.o.) ; the upper tract becomes the soft selvedge 
of the short hind skull, up to the single, very large, pear-shaped fontanelle ( fo .), the 
broad end of which it encloses. 
The lower tract passes into an extensive cross-shaped field of cartilage, not divided 
off from the unossified interorbital part (fig. 2). Thus we have the normal division 
into prootics and ex-occipitals (fig. 2, e.o. to II.). These, however, are anchylosed 
together on the epiotic eminence (fig. 1 p.s.c.), but a narrow band of the roof-cartilage 
runs along almost to the end of this rounded balk. The parotics are ossified to 
their end, leaving but little cartilage even at the tegmen. The prootics enclose the 
foramina ovalia (V.), and almost touch the optic fenestra (II.). The ex-occipitals run 
up to the fenestra ovalis, but the outer part of the vestibule (fig. 2, vb.) is floored with 
cartilage, which is continuous with the soft part of the basal plate (b.o.). The 
girdle-bone (eth.) is equal to the unossified tract behind it, yet their junction is not 
in the middle of the orbits, but further forwards, for that bone runs a little into the 
proper nasal region (s.n,). Yet it does not harden the wings of the ethmoid, nor the 
narrow superorbital eave (s.ob.). The endocranium in the orbital region is, as to its 
cavity, very similar to that of H. alhomarginata (see Plate 32, figs. 6, 7 ; and Plate 33, 
MDCCCLXXXI. 2 B 
