DEVELOrMENT OF THE SKULL IN THE BATRACHIA. 175 



Divergence from the " norma " is seen in : — 



1. The general breadth and depression of the skull. 



2. The thorough continuity of the endo-craniul bones of the hind skull, above, and 

 of those of the same side, below. 



3. In the mid skull the great size of the optic fenestra, and the limited extent of 

 the girdle-bone. 



4. The superorbital eave, and large single fontauelle. 



5. In the fore skull, the large, well made prenasal, and the unusual size of the pro- 

 rhlnals. 



G. The stylo-hyals and supra-stapedials are confluent, above. 



7. The fronto-parietals are arrested. 



8. The basal plate is very small, and the thyro-hyals very large. 



48. Hyla alhomarginata. — Adult female ; 2^ inches long. Brazils. 



This species, which is nearly twice as large as those whose skulls have just been 

 described, cannot be far removed from Phyllomedusa, in spite of its want of "pai-otoids." 

 Its skull is moderately strong in its outworks ; the endocranium very strong, although 

 very flat ; the ethmo-nasal region takes up half its length, and this causes it to be 

 almost a long skull, the breadth being only one-fiftieth greater than the length ; the 

 jaw-hinge reaches very nearly as far back as the occipital condyles. 



Thus much of the divergence from the type is in this kind evident at first sight. 

 Besides its Hkeness to the skull of the gigantic South American kind, it resembles 

 very much that of an Australian svib-type, namely, Litoria marmorata (see Plate 19, 

 figs. 11, 12 ; and Plate 32, figs. G, 7) ; but the skull of that species is much less unlike 

 the " norma." 



Even here the Ranine skull is but thinly veiled, and not so much metamoqihosed 

 in any part as to hide its fundamental character ; and yet this normal form is an 

 acquired character, whUst the primary form was Pctromyzine, or " Suctorial." 



The occipital condyles (Plate 32, figs. 6, 7, oc.c.) are small, subreniform, and postero- 

 inferior ; they are separated by an interspace which is greater than their own width, 

 and this is deep and crescentic ; the epiotic eminences (p.s.c.) are nearly flush with 

 them. 



A line drawn athwart the middle of the hmd brain, and cutting the junction of the 

 anterior with the posterior canals (a.s.c, p.s.c.) would also run across the opening of 

 the tyrapano-Eustachian cleft (ew.), where the columella pushes out its extra-stapedial 

 process (e.st.) ; this point is a little behind the middle of the drum of the ear (a.ti/.). 

 The great parotic wings are half the breadth of the rather small proximal region of the 

 auditory capsules ; they turn a little forwards, externally, but they are dilated somewhat 

 along tlie tegminal margin (fig. G, under sq.). 



The ossification of the hind skull is continuous everywhere, except a short oblong 



