DEVELOPMENT OF THE SKULL IX THE BATRACHIA. 49 



evident " pterotic " eminence projecting behind the squamosal, at the end of the 

 tegmen tynipani (fig. 1, sq.). 



The form of the canals within is less obscured by the bony gi'owths and coverings 

 than in tlie 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, «.), 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 naiTowness of this trough approximates to what I shall show 

 in my next instance but one, viz. : in Hana pipiens (Plate 8). 



Here, again, a small superoi-bital projection {s.oh.) Ls 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. teniporaria ; 

 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 {71. 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 G, fig. 2,p)a.) 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,pd.) 

 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-jugal (7./). 



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 their inner edge is sinuous, not arcuate. 



Tlie fronto-parietals (fig. \, f-p.) are less dense, are distinct in their fore half, and 

 the temporal fossa? are bounded, above, each by its own parietal ridge ; the hinder 

 spreading part is altogether less. 



The nasals («.) are larger, broader before and beliind, and their facial process (fig. .3) 

 forms a more perfect suture with the maxillaiy. 



MDCCCT.XXXl. H 



