DEVELOPMENT OF THE SKULL IN THE BATRACHIA, 
163 
The thyro-hyals (t.hy.) are as long as the basal plate at its middle ; they are slender, 
straight, moderately divergent, and well ossified. 
The investing bones are thoroughly Cystignathine, and very elegant; the fronto- 
parietals (fig. 7,fp.), are dilated in the temporal and ethmoidal regions, are hollowed 
out to form the temporal fossa, and spread well over three-fourths of the hind skull, 
where they end by a straight margin. They widen steadily in the orbital region, and 
taken together, their fore-edge is crescentically emarginate—so much so that the great 
fontanelle is not quite covered, and a large lozenge-shaped tract of the girdle-bone is 
left naked. The diverging outer angle of each lies on the corresponding nasal. The 
nasals (n. ) have the normal shape; they are large, convex shells, and each touches the 
septum nasi by its inner edge; their bluntish fore ends leave the snout uncovered for 
some distance. 
The marginal bones ( px ., mi, q.j., sq.) are well developed and perfectly normal; the 
squamosal, however, only lies on the edge of the tegmen tympani; its post-orbital 
process is bent outwards, and is curved and long ; the descending part is normal. 
There is a very small, sesamoid septo-maxillary (fig. 7, between u.l 2 . and al.n.). 
The parasphenoid (fig. 8, pa.s.) is long, well-developed, and normal; the bone is 
thickened at the cross, and the transverse processes are carinate, the thickening 
running along them as a ridge; the “ handle ” is unusually long and slender. 
The vomers (fig. 8, v .) are very large triradiate plates; there is a y>os£-narial, but 
not a yme-narial spur; and the front part is triangular, running under the edge of the 
dilated subnasal lamina (right and left of s.n.) ; these, right and left, are far apart. 
The hinder half of each bone, on the contrary, converges towards its fellow, each 
almost reaching the point of the parasphenoid. From the hind margin a thick rib 
grows, covered with a rasp of retral teeth; these lobes reach outwards further than 
the inner edge of the inner nares (i.n.), their thick end is outside, and they are 
furthest forward there. This hind margin is slightly arcuate, so that they run across 
the fore palate as a crescentic rasp, j ust broken at the mid-line; they are quite 
Cystignathine. 
Most of the divergencies from the “ norma” in the skull in this species are very 
gentle, and yet quite appreciable ; this is a true Neotropical Frog, with the toes dilated. 
Its main points of difference are as follows :— 
1. The nasal region is extremely large, both wide and long; and the orbital region 
steadily widens towards it. 
2. The hind skull is unduly ossified. 
3. The prootic region has a projecting spike, as in Siren lacertina , and the larva of 
Triton cristatus. 
4. The palato-suspensorial arch is very slender. 
5. The quadrate is largely ossified. 
6. The annulus is small and widely open. 
7. There is neither an inter- nor a szfpra-stapedial. 
Y 2 
