40 MR. W. K. PARKER ON THE STRUCTURE AND 



Skulls of adult individuals of the genus Raua. 



((. European species. 



6. Rana tenij)oraria. 



I have just referred to the characters of this (typical) species, described and figured 

 in my first paper (Phil. Trans., 1871, Plates 3-10, pp. 137-211). I shall use it as 

 a norma, after eliminating its one aberrant chai'acter, viz. : its sub-distinct " meta- 

 pterygoid."'"' 



7. Eana esculenta. 



For a description of the skull of this species the reader is referred to Professor 

 Huxley's article on the "Amphibia" (Encyc. Brit., vol. ix., pp. 750-77 l).t 



h. Oriental species. 



8. Rana gracilis. — Adult male ; 1^ inch long. Ceylon. 



The skull in tliis small species (Plate 6, figs. 6-10) difters but little from that of the 

 Common Frog (op. cit., Plate 9) ; its endocranium is more ossified, but its mandibular 

 hinge does not reach so far back : the general form is very sunilar, being half a rather 

 long elhpse. Between the oval occipital condyles there is a large right-angled space 

 (figs. 6, 7), and the outline of the foramen magnum {f.ni.) above is a large crescentic 

 emargination. 



The superoccipital soft tract is twice as wide as the basioccipital, but they are both 

 of small extent. The whole occipito-otic mass is a large transversely-placed oval, the 

 ends of which are nearly ossified above, but with a large tract of cartilage below, which 

 runs across from side to side between the prootics and ex-occipitals {j^r.o., e.o.). The 

 passages for the main nerves (II., V., IX., X.) are large and veiy clearly seen in tlie 

 lower view (fig. 7). The optic nerve passes through a large membranous fenestra, 

 which has a narrow tract soft behind it, and a broad tract in front ; half the inter- 

 orbital region is unossified, but the foramen ovale (V.) lies in the centre of the large 

 postorbital face of the prootic. 



Above, from beyond the horizontal canal to the edge of the tegmen tympani, there 

 is a soft tract ; but from thence inwards to the lesser fontanelles all is bony, and 

 the prootics and ex-occipitals are quite blended, walling in the canals and covering 

 most of the hind archway of the skuU. The fore half of the interorbital region is 

 occupied by the common " sphenethmoid," or gu'dle-bone (eth.), which does not take 

 up all the ethmoidal region ; it projects in front above, but is emarginate below. The 

 fore part of the ethmoid, all the nasal region, and the transverse ethmo-palatine bars 



* In my figures of the nasal region of this species (" Batrachia," Part 2, Plate 54, figs. 1, 2) the 2nd 

 upper labial is figured too high up, and the pro-rhinals are lettered c.tr. 



t This species has the pro-rhinals distinct, as Professor Huxley's figure (p. 755, fig. 9) correctly .shows. 

 This distinctness is seen again in Dadylethra (Phil. Trans., 1876, Plate 59, fig. G, u.l".) ; it is there 

 lettered u.V. by mistake. 



