DEVELOPMENT Ol<' 'J'llE SKULL IN TIIK BATRACHLV. 173 



and also tlie squamosals (.svy.), are very similar to those of the last kind; there is a 

 small club-shaped septo-maxillary (fig. 6, s.iax.) on each side under the second upper 

 labial {ii.l'~.). The parasplienoid (fig. 7, pa.s.) is altogether more slender and pointed 

 than that of//. Ewiiujii, especially in its basi-temporal spurs. The vomers (fig. 7, v.) 

 are large ; they have a curiously-arched form, a deutigerous lobe twice as large as in 

 the last, and come nearer together. The postero-external edge of the bone embraces 

 half of the great inner nostril, and the outer spike in front of this passage is but the 

 hinder uf a series of tootli-like projections of the bone. 



The difference between this skull and that of the "norma " is much the same as in 

 the last ; it comes nearer, however, to the pattern -form, in having the ex-occipitals and 

 prootics somewhat marked out, and in having the lateral masses of bone distinct ; also 

 in having septo-maxillaries. It diverges further in one thing, namely, in having a 

 basi-branchial rudiment projecting beyond the basal plate. Both the annulus and 

 columella, in these two kinds, come equally short of that which is typical. Here, also, 

 we have the optic fenestra and the superobital, both twice as large as in //. EiriiKjii. 



On the whole, there are about the same number of points in this and the last, in 

 which these typical Hjlce disagree with the " norma." 



47. Ilyla arhorea. — Adult male ; 1^ inch long. South Europe. 



This is a semi-oval skull, still shorter and broader than the last ; the breadth is to 

 the length as G to 5. 



On the whole, this specimen comes very near to //. Ewlinjil, notwithstanding the 

 distance between the homes of the two species. 



The skull is not quite so depressed as in the two last, and is rougher and stronger 

 in its general build ; also it is more fully roofed in. 



The occipital condyles (Plate 32, figs. 1 and 2, oc.c.) are larger and wider apart ; 

 they are postei'o-inferior, as in H. Ewin'jii. 



As in that sj^ecies, the occipito-otic ossifications are fused together, but in this kind 

 there is a basioccipital tract of cartilage (fig. 2, h.o.). 



The canals are larger, but the parotics are similar in both ; there is very little 

 imossified cartilage near the fenestra ovahs in this species ; altogether the ossification 

 is more intense above than below ; the bone encircles the foramen ovale (V.). 



The three regions of the skull are nearly equal ; the single fontanelle (/b.) is exactly 

 one-third the length from snout to occipital condyles ; it is an irregular oval, for the 

 edofes of the teirmen cranii are sinuous. 



The short, wide, depressed mid skull lessens a little from the temples, and enlai-ges 

 again uito the superorbital lobes, which are ossified, proximally, by the girdle-bone 

 (s.oh., eth.), and are semi-oval, not pi'ojecting nuich more than in //. Ewnujii. 



The girdle-bone scarcely occupies a third of the mid skull ; and the large optic 

 fenestra (II.), which is intermediate in size between that of the two last, is well 

 martrined with cartilasje. 



