DEVELOPMENT OF THE SKULL IN THE BATE AC HI A. 
I 93 
They then become narrow bands, and in front turn outwards, over the superorbital, 
which they partly cover; their end is truncated. By this divergence the girdle-bone 
is left naked, and the fontanelle is scarcely covered at all by them. 
The nasals (n.) are rather small shells; they have a falcate outline, and are notched, 
behind; the hollow blade overlies the very limited nasal roof. The marginal bones 
are well developed; the nasal process of the premaxillary ( px.) is thick, wide, and 
high ; it is capped by the small 1 st labial. 
The maxillary (rnx.) is very high in front, and rather high behind; where it shelves 
downwards, over the premaxillary there is a small, notched septo-maxillary (s.mx. ); 
the quadrato-jugal (qj.) is normal in size ; it is largely continuous with the quad¬ 
rate (q.). 
The squamosal (sq. ) has a long falcate upper part, and a long, broad, retreating 
lower part. 
The parasplienoid (figs. 2, 3 , pa.s.) is large, smoothly convex below, and has all its 
four rays pointed. 
The vomers (fig. 2, v.) are at their highest development; they occupy all but the 
fore margin of the very wide subnasal cartilage, and as the large circular inner 
nostrils (i.n.) are wide apart, there is a large inter-narial space for the two vomers, 
which fit, by “harmony,” along the mid-line. 
Each bone sends a narrow sharp snag out in front of the passage, and in front of 
this a broader falcate process. 
But each bone has a large oblong body, with a rounded front, and a nearly straight 
hind, margin; this part is thickened into a smooth, rounded mass, whose hind margin 
bristles with retral teeth. 
This toothed lobe projects a little further backwards on the outer, than on the inner, 
edge. 
At first sight it would seem difficult to make out many points of difference between 
this skull and that of the two European species of the typical Frog ( Rana), for the 
size is intermediate between the two, and the elements are essentially the same in this 
and in them. 
Nor are the relative proportions of the three regions of the skull different in any 
remarkable degree; nor the proportionate quantity of bone to be found in the endo- 
cranium. 
Carefully compared with the type, this skull is seen to differ in the following 
respects, namely:— 
1. There is a very distinct post-auditory arch. 
2. The parotic wings are of great extent, and give off a long “ pterotic ” process 
postero-externally. 
3. Each lateral mass of bone has lost all signs of division, above. 
4. The mid skull is very flat, has wide tegminal margins, and has one moderate 
fontanelle. 
2 c 
MDCCCLXXXI. 
