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



confluent, but the main part of it has been absorbed (tig. 4), otherwise, the basal plate 

 is typical. 



The "annulus-tympanicus" is large and a complete ring (fig. 1 a.ty.), the Eustachian 

 openings (eu.) are large, oval, and oblique. 



The greater part of the difference between this skull and that of the Common Frog 

 depends upon the intensity of ossification and the large size of the investing bone.s — 

 all correlated to the great size of this type. Other more important differences there 

 are, viz. : — 



1. A definite prenasal rostrum. 



2. No " septo-maxidaries ; " the nasal cartilage ossified in that region. 



3. A crested dentary. 



4. Much of the cerato-hyals absorbed. 



5. Stylo-hyal end of these bars confluent, above. 



6. Supra-stapedial confluent, above. 



7. Quadrate partly ossified. 



8. Rudiment of superorbitaL 



12. Rana hexadactyla. — Adult female ; 5^ inches long. Ceylon. 



This specimen was a little less than that of R. tigrma, and the skull (Plate 7, 

 figs. 1-5) is slightly longer, but its greatest breadth is only as 8 to 8f ; the quadrate 

 condyles only project one millimetre, or about half a " line " beyond the occipital 

 condyles ; in R. tigrina they project twice as far backward. 



In outline, besides its narrower form, the nasal end is broadly truncate, and these 

 two modifications cause a third, viz. : the unusual straightness of the sides of the skull. 



It is altogether a feebler skull, with less intense ossification, as well as being 

 straighter and narrower ; moreover, it is not quite symmetrical ; yet its facial plates 

 (fig. 3, mx., sq.) are deep and well developed. 



But these are mere superficial differences between the two ; there are others that 

 lie deeper down. Gentle enough are these moi-phological variations, and no bar to the 

 supposition that the two species originally spnmg from one common stock, yet they 

 are not to be lightly passed over, for they are full of interest. 



The occipital cond^des {oc.c.) are rather larger and more under the skuU than in the 

 last ; also the emargination between them is deeper, these are due to some differences 

 in the workingr of this hinjre. 



The whole occipito-auditory mass is less oblong, its front faces being oblique as they 

 pass into the interorbital region, exposing the foramina ovalia (V.), and the occipital 

 condyles and epiotic eminences {ep.) over the posterior canals project more backwards : 

 moreover, the bones of the two sides are confluent over the foramen magnum {f.m ). 



Yet there is more cartilage between the 2nd and 5th nerves (II., V.), and also a more 



