DEVELOPMENT OF THE SKULL TX THE BATRACHIA. 263 



palatine is always a distinct cartilage and rather late in appearance ; the pterygoid 

 cartilage is in the Urodele an outgrowth from the suspensorium — a little later in 

 appearing ; the post-palatine is a separate cartilage, also. 



The hinge for the jaw is in them, at first, just where it gets to be in the trans- 

 forming Tadpole, when the tail is nearly absoi'bed ; the cerato-hyal has in that stage 

 the same position it has, at first, in the embryo of the Urodele. There are no lalnals, 

 no extra-branchials, and no spiracnlar cartilage in the Urodeles,'"' and they develop 

 three ov four true iViira-branchial arches. 



The floor is never finished with cartilage any more than the roof; the former is 

 often divided into two compartments by the persistence, for a long period, of the 

 apices of the ti-abeculfe, which keep separate from the posterior parachordal tracts. 



In one species (viz. : Ranodon sibiricus ; see Wiedersheim, " Das Kopfskelet der 

 Urodelen," plate 5, figs. 69, 70), the palato-quadrate arch becomes continuous ; an 

 exception similar to that of Bifo vulgaris, where it becomes segmented. 



The frontals and parietals are always long narrow bones ; the paraspheuoid is a 

 broad generalised plate ; the vomers and palatines are both dentigerous ; the latter 

 become strangely transposed, during metamorphosis, in the " Caducibranchiata." 



The quadrate ossifies of itself, and there is neither a quadrato-jugal nor a jugal ; the 

 bony arch of the cheek is always (as in the Anura Aglossa and Teleostei) unfinished. 



The squamosal has no postorbital process, but it has, at times, a very distinct lower 

 supratemporal j^rocess. The premaxillaries are generally double ; and sometimes there 

 is only one. The maxillaries ai-e large m the higher, but small, or even suppressed, 

 in the lower, types. 



Besides the cerato-hyal, and its lower hypo-hyal segment or segments, united by 

 a distinct basi-hyal, there is in the larger and some of the smaller kinds, an epi-hyal 

 element, not infrequently subdivided, so as to show a " pharyngo-hyal " also. This 

 last is found in the " suspensorio-stapedial " ligament, and the former in the " hyo- 

 suspensorial ;" the upper piece answers to the pharyngo-hyal of the CIdmcera, and to 

 the inter-stapedial of the Frog; the lower piece to the epi-hyal of the one, and to 

 the medio-stapedial of the other.f 



Even this very imperfect comparison of the skull of the Urodeles, with what we 

 have just seen in the Anura, shows how far these groups are apart, notwithstandincr 

 their many points of similarity ; a thorough comparison of the larval skull of the latter, 

 with that of the Lamprey, will be given in my next communiaition, which will treat 

 of the cranio-facial skeleton of that Fish. 



• In my paper on the Urodeles (Phil. Trans., 1877, p. 587) I expressed an opinion, now found to be 

 wrong, viz. : that the cartilage which in some Urodeles passes from the suspensorium to the stapes was 

 the same a-s the " spiracular cartilage " of the Tadpole. 



t In Raiui halecina and R. palustris (Plate 5, figs. 5 and 10) I have shown the Acipenserine 

 subdivision of the Frog's columella; of course the "inter-stapedial" is due to the normal subdivision of 

 the proximal piece. 



