DEVELOPMENT OP THE SKULL IN THE BATRACHL\. 185 



The outline is semi-oval, and tlie length is to the hreadth as 10 to 11 ; the hinge 

 of the jaw has got no further back than the end of the u])per bar of the squamosal 

 (sq., q.c), in this it is in strong contrast with the skull of Ilyla alhomanjinala. 

 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 tympaui 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 akuU 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 A\-ith the basi-fticial hue ; and there is a great obliquity of the 

 squamosa] {sq) outlying it, the hammerlike head of wliich is tilted downwards to 

 articulate mth the jvigal process of the maxillary. 



Without any loss of elasticity — for soft triicts of cartilage alternate with hard 

 teri'itories of bone — tiiis skull is one of the strongest, for its size, of any to be foinid 

 in the " Order ;" albeit, like that of a Crocodile, it retains not only much cai-tilage, 

 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 ; tliey 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 (behmd_/l2^- ^^^^ '^^ h.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 held of cartilage, not divided 

 oft' from the rmossitied interorbital part (fig. 2). Thus we have the normal division 

 into prootics and ex-occipitals (tig. 2, c.o. to II.). These, howevei-, 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 paretics are ossified to 

 their end, leaving but little cartilage even at the tegmen. The prootics enclose the 

 foramina ovaUa (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, vh.) is floored with 

 cartilage, which is continuous with the soft part of the basal plate (h.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 superorliital eave {s.oh.). The endocranium in the orbital region is, as to its 

 cavity, very similar to that of II. alhomarcjinata (see Plate 32, figs, fi, 7 ; and Plate 33, 



MDCCCLXXXI. 2 B 



