48 
MR. W. K. PARKER OK THE STRUCTURE AND 
confluent, but the main part of it lias been absorbed (fig. 4), otherwise, the basal plate 
is typical. 
The “ annulus-tympanicus” is large and a complete ring (fig. 1 ci.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 bones— 
all correlated to the great size of this type. Other more important differences there 
are, viz. :— 
1. A definite prenasal rostrum. 
2. No “ septo-maxiilaries ; ” 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. tigrinci, 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 morphological variations, and no bar to the 
supposition that the two species originally sprung from one common stock, yet they 
are not to be lightly passed over, for they are full of interest. 
The occipital condyles ( oc.c .) are rather larger and more under the skull than in the 
last ; also the emargination between them is deeper, these are due to some differences 
in the working of this hinge. 
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 (fm ). 
Yet there is more cartilage between the 2nd and 5th nerves (II., V.), and also a more 
