DEVKLOPMENT OF THE SKULL IN THE BATRACHIA. 125 



fonner [si.) i.s a solid, sub-pcduncukite mass, sub-oval in form, but scooped to receive 

 the columella. This latter part has no separate iater-stapedial segment ; but there 

 is a large thick unossified lobe to the end of the medio-stapedial {in.st.) which 

 represents it. Between this and the main stem there is a deep notch, faced fore and 

 aft with cartilage, then the bony bar gradually lessens, is arched, and ends in a terete 

 rod of cartilage which dilates into the thick, oval, bi-convex extra-stapedial (e.st.). 

 From the inner face of this lobe there arises, at a sharp angle, the terete, stout supra- 

 stapedial (s.st.), which is confluent with the " tegmen " above. 



The stylo-hyal end of the cerato-hyal (figs. 2 and 4, st.Ji., c.liij.) seems like a flabelli- 

 form continuation of the vestibule; it is wide at first, then naiTows as it passes directly 

 outward, margining the Eustachian opening ; is then wider again as it creeps along 

 the inside of the quadrate, and after this becomes a little less again, as it passes, 

 sigmoid in form, to the hypo-hyal region (h.hi/.). There is no enlargement, but it 

 forms a round loop, and then gently dilates as it passes into the basal plate 

 (fig. 4, b.h.br.). 



The antero-posterior extent of the basal plate is small, as in the " Hylidee ;" its lobes 

 are large, the foremost flabelliform, the hindmost — here quite as large — is stalked 

 and emarginate. There is no bone, save in the " thyro-hyals " (f.ht/.); they are of 

 moderate length, divaricate w'ell, are stout, and soft-footed. 



This skull, with its sti-ong roof and sides, is constructed, externally, of seven pairs 

 of bones, and an odd one ; in the young the main roof-bones were divided across, which 

 gi ves seventeen " parostoses " originally investing the proper endocranium ; the plates 

 appUed to the cartilage, and grafted upon it, are not counted, but the two " dentaries " 

 in the lower jaw bring the sum up to nineteen. The other bony tracts in skull and 

 face amoimt to seven pairs and an odd one — that, however, the girdle-bone, was double 

 once, so that there are sixteen bony centres that are properly " endoskeletal ;" in all, 

 there ^oer^ thirty-five ; there are thirty-two bones in this skull. 



But the " quadrato-jugal " is grafted on the quadrate and becomes partly endo- 

 skeletal, whilst, on the other hand, the bony centres that were formed in the chondro- 

 cranium (ex-occipital, prootic, &c.), are largely recruited, in their gi'owth, from the 

 perichondrial layers of membrane, thus they link on to the palatine and pterygoids 

 that begin in membrane, and get their "endosteal" additions afterwards. But the 

 truly parosteal " sub-species " of bony centre concerns us now ; I shall describe this 

 group, and then show what was the form of the original " chondrocranium," on and 

 in which this strong architecture is perfected. 



Behind, the roof-bones come close to the edge of the foramen magnum [f.m.), and 

 are built acro.ss from side to side, without interruption, over the condyles of the 

 quadrate region ; the hind margin of this wide ti-act is emarginate, crescentically. 



The nasal, frontal, and saggital sutures form one line of division from snout to 

 occiput, and each region of this long suture is, about equal. The two pairs of main 



