412 



HARRIS HAWTHORNE WILDER ON 



evident and presented a similar appearance in a series taken from a larva of 26 mm. This 

 observation, which seems perfectly clear and unassailable, and wliicli corroborates the 

 results given by Stohr in other Urodeles, is absolutely at variance with the statement of 

 Miss Piatt, who says that " it arises independently " and identifies as its anlage a mass of 

 cells which, in an emln-yo of 19 mm., is situated just in front (outside) of the fenestra 

 ovaUs, and between it and the end of the ceratohyal. It is possible that tliis anlage 

 may represent a true columella or hyomandil^ular cartilage, wliich may later become 

 fused with the true operculum to form its projecting external process, although in 

 the larvae of 26 mm. and 44 mm., the series which I have examined, I can find no 

 trace of such a double origin of the parts in question. 



The brain case. — This is formed in great part by five dermal bones, the two frontals, 

 two parietals, and the parabasale, of which the first four form its dorsal, lateral, and ante- 

 rior walls, and the parabasale its floor. The box formed by these is deficient poste- 

 riorly, where it is completed by the otic capsules and other cartilaginous elements with 



their ossified areas. Above, each 

 frontal is so completely welded to 

 its accompanying parietal by means 

 of interlocking splints that they practi- 

 cally form one bone while the two sets 

 of united pairs meet in the median 

 line by means of somewhat tliickened 

 flat edges, forming symphyses. Upon 

 the ventral surface of this roof, both 

 bones end down extensive processes 

 that lie just within the trabecular 

 arch of the primordial skull and make 

 an extensive ridge in the form of a 

 long narrow U, the loop being directed 

 anteriorly. This lidge forms the 

 front and sides of the brain case and 

 at its ventral edge is everywhere 

 in contact with the parabasale. 



The result of this singular forma- 

 tion is that in Necturus the lateral 

 walls of the brain case are formed of 

 solid dermal bone reinforced exter- 

 nally by cartilage while in most Uro- 



4y * ^*tll» from 





Pot.fijn of- 



X PS [~ O'lirt-ifheniiJ 

 Procesj of PorietalJ 



Fig. 12. The roof of the brain case seen from beneath. X 3. 

 Til is is composed of the two frontals and the two parietals, upon 

 the ventral side of which is developed a series of processes which 

 together form a U-shaped ridge that forms a front and sides to 

 the case. Contact surfaces for other bones are designated by an 

 X and the abbreviations of the bone involved. 



