or THE SKULL IN THE UEODELOUS AMPHIBIA. 719 



metabolous types) is afc first dentigerous, and then sends an 

 edentulous process backwards ; the bone cuts off this latter 

 process, and then the two pieces become diversely applied to 

 the skull proper. Tho tooth-bearing part, directly behind the 

 corresponding vomer, either grows directly outwards beneath 

 the ethmo-palatine cartilage or directly backwards beneath the 

 basis cranii. 



The latter condition is seen generally in Salamanders and 

 Newts, which have a long dentigerous submesial palatine ; the 

 former modification is seen in Amhlystoma ; but in Sperlepes and 

 Besmognathus we have these two modes combined. The edentulous 

 bone applies itself to the pterygoid process of the suspensorium 

 and to the inside of the body of the suspensorium (quadrate region). 



In the Anura the pterygo-palatine cartilages are developed as 

 one, and only become segmented rarely, as in Bufo vulgaris ; but 

 the bones are always developed independently, and not by the 

 breaking-up of a simple primordial pterygo-palatine plate. 



The transformations of the Anura are carried on in the plastic 

 larva and young to a greater extent than in the TJrodela. 



In the Anura the opercular ray of the mandibular pier (the 

 "spiracular cartilage " of the Shark) becomes the annulus tym- 

 panus, and a late-appearing hyomandibular becomes, by trans- 

 formation, the columella auris. 



In the Urodela the hyomandibular only occurs in the lower 

 tj^pes ; it is suppressed in the " Metabola" or Caducibranchs. 



But some of these have n, pseudo-columella, not Ijing under the 

 facial or seventh nerve, as any part of the hyoid arch must, but 

 over it, in the opercular skin. This spiraculo- stapedial bar (seen 

 in Menopoina, Spelerpes, and Desmognatlms) is of great interest, 

 as showing how little function is to be trusted in morphology. 



There have not been wanting anatomists who, failing from 

 deficient embryological knowledge to see to the meaning of this 

 or that part, have trusted to teleological explanations ; but teleo- 

 logical science, belonging to another category of research and of 

 thought, thus used, becomes a misleading light — an ignis fatuus. 



