AMPHIBIA. 397 



quadrate which is forwards and downwards in Proteus and the lower 

 Urodela, backwards and outwards in Anura. The hyoid of Urodela 

 consists of a ceratohyal and generally a hypohyal element : it is united to 

 the quadrate and stapes by ligament. In Anura it generally resembles 

 that of the Frog (p. 81), and is continuous with the floor of the tympanum. 

 The Urodela have four branchial arches, the two posterior rudimentary 

 and in adult Salamanders lost. There is in them a basi-hyo-branchial as 

 well as a basi-branchial copula. The larval Anura have four branchial 

 arches represented by four rudimentary cerato-branchial elements, but 

 there are also four large extra-branchial cartilages united at their dorsal 

 extremities and lying subcutaneously. 



The skull in Gymnophiona is remarkable for the large size of its bones, 

 and for the very complete case they make. Epicrium has a ring of orbital 

 bones like the Stegocephali. The mandible articulates with the quadrate 

 by a concave surface as in Fish. The skull of the extinct Stegocephali is 

 similarly complete. It has remarkably large epiotics and paired supra- 

 occipitals (not homologous probably with the supra-occipital generally 

 so-called). There are prae- and post-frontals, post-orbitals, and a supra- 

 temporal which lies externally to the squamosal. A jugal and quadrato- 

 jugal are nearly always present. The dorsal surface of the skull is often 

 polished and sculptured as in many Ganoid fish, and in this respect it is 

 approached by a few living Anura, e.g. Pelobates 1 . Remains of two 

 branchial arches have been discovered, and there is reason to believe that 

 they persisted in some adults, e.g. Branchiosaurus, whilst they are lost in 

 others, e.g. Melanerpeton. 



The vertebral column contains a large number of vertebrae in Ichthy- 

 oidea and Gymnophiona (250 or more) ; a more restricted number in 

 Salamanders ; and in living Anura only eight praesacral vertebrae and one 

 sacral with a coccygeal style. It is divisible into a cervical, thoracic, 

 sacral and caudal series in Urodela. A single more or less ring-like cervical 

 vertebra devoid of ribs is found in all Amphibia. In most Urodela it carries 

 a well-marked ' odontoid ' process, traces of which are sometimes seen in 

 Anura, and which points to the loss, partial or complete, of an anterior 

 vertebra. The remaining vertebrae carry in Urodela double transverse 

 processes, the upper, feebly marked in Gymnophiona, an outgrowth of the 

 arch, the lower of the centrum. They become rudimentary in the tail. 

 These processes are single in Anura. Articulating processes are well 

 developed. The neural arches are in living Amphibia anchylosed to the 

 centrum. The neural spines are almost obsolete in Anura, but in Urodela 

 they are prominent, sometimes forked terminally and articulating one with 

 another; or, in Salamanders, flattened sideways, lamelliform and comb- 

 like, a condition which obtains in some Stegocephali (Nectridea), where the 



1 The significance of the channels, sometimes termed ' mucous- canals,' on the face in certain 

 genera of Stegocephali is not known. 



