DEVELOPMENT OF THE SKULL IN THE RATRACHIA. 171 



1. The extremely flat form of the skull, generally. 



2. The intense ossification of the occipito-otic and ethmoidal regions. 



3. There is but one, that a very large, fontanelle. 



4. The prenasal is present, and the lesser cornua (pro-rhinals) are half the size of 

 the outer angles of the snout. 



5. The superorbital tract is distinct as a semi-oval eave, 



6. The nasal roof is very nari'ow, as compared with the floor. 



7. The annulus has its homs wde apart. 



8. The pedicle is very sohd, and the Eustacliian opening is margined behind by a 

 confluent stylo-hyal. 



9. There is neither a separate inter-stapedial nor a supra-stapedial band. 



10. There are no lobes on the hypo-hyals, and no antero-lateral lobe on the very 

 small basal plate. 



11. The roof-bones are extremely arrested and narrow. 



12. There are no septo-maxillaries. 



46. Hyla phyllochroa. — Adult female ; 1 inch 5 lines long. Cape York, Australia. 



This skull resembles the last very much, but is altogether frailer, and less ossified ; 

 I am not aware of havmg dissected a skull more light and delicate than this ; its main 

 rivals are some of those of its own country, \\z. : Rappia hicolor, and Camariolius 

 tasmanietisis. 



The outhne of this skull (Plate 31, figs. G-9) is elegantly semi-oval; it is much 

 shorter than the last, the breadth being to the length as 7 to G, and the condyles of 

 the quadrate have retreated much further back, being opposite the proximal part of 

 the occipital condyles. These condyles project as little as in the last, are smaller, and 

 differ in direction, being exactly posterior. 



Both skulls are equally depressed, but this differs in shape in all the three regions. 

 The auditory capsules are only three-fourths the size of those of //. Ewingii; the 

 paretics project much further outwards, and are considerably narrower. 



The tegmen cranii reaches more than half-way from the foramen magnum to the 

 front of the cavity, and runs round the single fontanelle {fo.) as a considerable band 

 both right and left and in front. The greatest width of this membranous space is 

 equal to that of H. Eivmgii and to its own length, but the widening backwards of the 

 marginal teamen makes it lose what would otherwise be the circular form. 



A large triangular tract of cartilage exists above, occupying most of the hinder 

 tegmen, and a clear synchondrosis exists both above and below at the foramen magnum 

 (/.m.) ; the floor of the vestibule and the tegmen tympani (fig. 7, vh.. and fig. 6, t.ti/.) 

 are also unossified. Above, there is a narrow tract of cartilage running from the 

 horizontal canal to the junction of the anterior and posterior canals (fig. G). In front, 

 the prootic bone reaches to the foramen ovale (fig. 7, V.) ; above (fig. 6), the bone 

 reaches the i-oof over the optic fenestra (II.) The girdle-bone (eth.) only occupies one- 



z 2 



