DEVELOPMENT OP THE SKULL IN" THE BATRACHTA. 191 



Tlie reasons for the great unlikeness of this skull to that of the type are not, at 

 first, easy to find ; the same elements are there, having the same relations, and the 

 degree of ossification of the chondrocranium, and tlie form and size and density of the 

 investing bones is very similar in both. The occipital condyles (Plate 34, figs. 1-4, oc.c.) 

 are reniform, and posterior ; they are of the average size, and are separated by an 

 emarginate space more than equal to their own diametei". The post-auditory part of 

 the skull is here unusually developed — there is tlius a " neck " to the skull, if there is 

 none to the body. Tlie " parotic wings " stretch out to an unusual distance, are of a 

 good breadth to their end, and are then dilated along the tympanic roof. 



Considerable super- and basioccipital tracts of cartilage remain wedge-like between 

 the lateral bones ; those of the same side ai-e perfectly confluent. 



Each occipito-otic bony ti'act reaches forwards from the condyle to the middle of the 

 space between the openings for the 2nd and 5th nerves (II. V.) ; laterally, the bone 

 is arrested a little beyond the horizontal canal (h.s.c.). 



There is, beyond the bone, an otic tract two-thirds the extent of the ossified part ; 

 this extended tegmen narrows gently, and then dilates over the ear-ckum, sending 

 outwards and downwards a pedate process, to which the hinder crus of the annulus is 

 attached behind the squamosal (figs. 1, 3, 4, t.ti/., a.ty., sq.). This postero-external 

 process is the familiar " pterotic ridge " of the Fish, and is weU seen, again, m Eana 

 jjijnens, and Cystignathus ocellatus. 



I find no secondary fontanelles, but in that region there is a considerable tract of 

 cartilage, triangular in shape, but with its apex truncated over the foi-amen 

 magnum. From that edge to the ossified tegmen in front, the roof, ossified laterally, 

 reaches neai'ly half way ; the fore half is occupied by the long oval main fontaneUe 

 {fo.) which is small, relatively, but almost entirely uncovered by the fronto-parietals 



if-P-)- 



This space is rendered naiTow by the marginal tract of endocranial roof, which also 



extends a good way back in the ethmoidal region. The mid skull has the hourglass 



outUne, for there is a considerable expansion of both the post- and antorbital parts of 



the roof, and the skuU is rather narrow where the girdle-bone {eth.) ends. 



Where the superorbital (s.oh.) cartilage overhangs the orbit, there the breadth, 

 above, is doubled ; but this is only where this ear-shaped flap projects ; it lessens 

 again and then is continued, roof-like, into the ethmo-palatine, as in Rappia hicolor 

 (Plate 19, figs. 6, 7). 



Above (fig. 1), the girdle-bone keeps to the narrow width of the mid skull ; but 

 below (fig. 2), it ossifies all but the superorbital flap, and takes uj) all the cartilage 

 belonging to it, both in the middle, and into the wings, right and left. 



In the fore skuU the nasal region is evenly rounded in front, and does not form a 

 square snout, with the nostrils (e.n.) wide apart, and at the edge, as in the Poly- 

 pedatida3 ; but these passages are sujDerior, and not very wide apart ; they are also 

 large, and have a strong rim of uncovered cartilage. 



