DEVELOPMENT OP THE SKULL IN THE HATRACHIA. 
49 
evident “pterotic” eminence projecting behind the squamosal, at the end of the 
tegmen tympani (fig. 1, sq.). 
The form of the canals within is less obscured by the bony growths and coverings 
than in the last, so that the general surface of this part is more uneven. 
The girdle-bone ( eth .) reaches from the optic fenestra to the middle of the septum 
nasi ( s.n .); it is therefore less in anterior extent, but it is visible between the 
vomers (fig. 2, v.), in front of the descending bar of the nasal (figs. 1 and 3, n.), and 
also behind that bar, ossifying the wing of the ethmoid up to the ethmo-palatine 
suspensorium. 
The whole interorbital part of the cranium is narrower and more pinched in the 
middle, and the relative narrowness of this trough approximates to what I shall show 
in my next instance but one, viz.: in Rana pipiens (Plate 8). 
Here, again, a small superorbital projection (s.ob.) is seen outside the meeting of the 
nasals and frontals, as in the last. 
In front, the prenasal is a mere bud, little more, pronounced than in R. temporaria; 
the pro-rhinals ( p.rh .) are much like those of the last kind. The outer angle of the 
subnasal lamina (fig. 1) is more extended and quite exposed, and this ( trabecular) 
plate also projects outwards further back, where the girdle-bone ends ; it joins the 
roof above by an ascending plate ( n.w .), which is ossified for some extent at its root. 
The labials are very similar in both species ; the upper is hidden behind the 
premaxillary. 
In R. tigrina (Plate 6, fig. 2, pa.) the palatines turn forwards and outwards ; in this 
kind they run straight across ; they also come nearer together; but on the whole 
these bones and the pterygoids (pg.) are very similar in both species : there is, however, 
more cartilage left unossified in this. The gliding joints of the pedicles (fig. 2 , pel.) 
are nearer together in this narrower skull, and the Eustachian opening ( eu.) is 
thrown obliquely backwards instead of forwards, outside, by the straighter hind 
process of the pterygoid. 
The hinge of the quadrate (q.c.) is less deep ; its substance is more ossified by the 
quadrato-j ugal (q.j .). 
Altogether the parasphenoid ( pa.s .) is slenderer and more elegant; it is equally sub- 
carinate, and has the blade and handle longer in proportion to the guard than in 
R. tigrina: here we see the most perfect form of this bone in the Batrachia, the basi¬ 
temporal processes being slender at first and then dilating outwards. 
The vomers (Plate 7, fig. 2, v.) are not so large as in the last, do not come so close 
together, and them inner edge is sinuous, not arcuate. 
The fronto-parietals (fig. 1, f.p.) are less dense, are distinct in their fore half, and 
the temporal fossae are bounded, above, each by its own parietal ridge ; the hinder 
spreading part is altogether less. 
The nasals (n.) are larger, broader before and behind, and their facial process (fig. 3) 
forms a more perfect suture with the maxillary. 
MDCCCLXXXl. H 
