OF THE SKULL IN THE AMPHIBIA UEODELA. 207 



and curious metamorphosis, both in form and in position, this bone yields the ossifyin°- 

 elements to each of these diverse and never united parts. Instead of repeating the 

 " labials " of the Lamprey and its relations, they have, both in their larval and adult 

 condition, the " median nasal cavity." Also, having no labials to metamorphose, they 

 have no superadded narial valves, and no ossified mento-Meckelian pieces in their man- 

 dibles. 



The premaxillary is often azygous. They have no " quadrato-jugal " binding the 

 maxillary to the quadrate ; they may have a small jugal, and a small additional tem- 

 poral ; both these exist in Amblystoma opacum. 



Equally with the Batrachia they have, as a rule, in the adult, no supra- nor basi-occi- 

 pital ; but two rudiments of occipital centra may exist for a few weeks of larval life, as 

 in Seironota perspicillata. 



Again, the Urodeles differ from the Batrachia in developing the curious intercalary 

 vertebra, the " odontoid " pre-atlantal rudiment. 



Their basal palatine, their palatine and sphenoidal teeth, their dentigerous splenial, 

 their distinct hypohyal, the formation of their thyrohyal from the dilated end of a median 

 branchial piece — all these things distinguish this lower tail-bearing group from the 

 higher tailless section of the Amphibia. 



Finally, there are curious dovetailings of the characters of the two groups : for 

 instance, there is usually no ossified quadrate in the Batrachia; it is exceptionally 

 unossified in one of the " Urodeles " {Siren lacertina). 



The divided state of the girdle-bone is seen in the anourous Pseudophryne Bibronii 

 and other Australian types ; these also have a rudimentary occipital centrum, or basi- 

 occipital. 



Pipa, like the Urodeles, has no quadrato-jugal, and has the quadrate ossification. 



The Bombinator (B. igneus) and Psexidophryne Bibronii have no columella; the 

 former and Pelobates fuscus have no " annulus : " all the " Anura" want this for a 

 time ; it appears at very variable periods in tbem. In the Urodeles the trabecule do 

 not, as a rule, develop a secondary cornu (prorhinal) from the inner angle, such as is 

 seen in Batrachia and embryo Sharks. 



APPENDIX. 



Since the above descriptions were written (latter part of 1877) my first paper on the 

 Urodelous type of skull has appeared in the Philosophical Transactions (1877, pis. xxi.- 

 xxix. pp. 529-597). Of my own finished work there still remains for publication after 

 this the development of the skull in the Common Newts (Triton cristatns, Lissotriton 

 punctatus), the skull of the adult Menopome, and of the half-grown and adult Siren 

 lacertina. But the MS. for the present communication was no sooner finished than 

 I received from Dr. Robert Wiedersheim, of Ereiburg, his two invaluable Memoirs on 

 these types. 



28* 



