AMPHIBIA. 275 



ries), and usually upon the vomers. In the urodeles teeth may 

 also occur upon the palatines, and occasionally upon the para- 

 sphenoid. In all cases they are firmly anchylosed to the sup- 

 porting bones. In the anuran tadpoles the jaws are covered 

 with horny plates. In the urodeles the tongue is rudimentary. 

 It is lacking in one division (aglossa) of the anura ; but in the 

 rest it is fixed in front, the bifid free end being turned back 

 in the mouth. It is capable of extension beyond the jaws, and, 

 covered with adhesive mucus, is used in the capture of food. 



The central nervous system has all of its parts lying in one 

 plane. The cerebrum is larger, and differs from that of all 

 fishes, even of the dipnoi, in the greater development of the 

 pallium. The olfactory lobes are in close connection with the 

 cerebral hemispheres. The cerebellum, on the other hand, 

 is reduced to a small transverse fold. The Gasserian and acus- 

 tico-facialis ganglia are distinct in urodeles and gymnophiona ; 

 but in the anura they are closely united, and the roots of the 

 corresponding nerves are not distinguishable by ordinary 

 dissection. There is a similar union of the glossopharyngeal 

 and vagus ganglia, and the common trunk of the ninth and 

 tenth nerves passes from the skull by a single foramen. In all 

 aquatic forms and larvae the lateralis branches of the seventh 

 and tenth nerves is well developed ; but with the assumption 

 of a terrestrial life these are lost, together with the lateral line 

 system which they supply (p. 67). 



The nasal passages form complete tubes, opening into the 

 oral or pharyngeal cavities by internal nares or choana in its 

 roof. Connected with the olfactory organs are well-developed 

 organs of Jacobson (p. 77). The epiphysial structures do not 

 extend beyond the skull in urodeles or gymnophiona ; but in the 

 anura the parietal eye lies between the skull and the skin, all 

 connection between it and the brain being lost. In the stego- 

 cephals there is a large parietal foramen in the skull, which 

 is interpreted as having contained a functional parietal eye. 

 The ears show an advance upon those of the fishes in the 

 development of a distinct lagena, 1 while the spiracular cleft, 



1 The lagena is the seat of audition, and recent experiments show that hearing first 

 appears in the amphibia. 



