OF THE SKULL IN THE UEODELOUS AMPHIBIA. 



710 



mctaboloiis types) is at first dentigerous, and tlicii sends an 

 edentidous process backwards ; tlie bone cuts oil' this latter 

 process, aud then the two pieces become diversely applied to 

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

 corresponding vomer, either growls directly outwards beneath 

 the ethmo-palatine cartilage or directly backwards beneath tho 

 has is cranii. 



Tlie latter condition is seen generally in Salamanders and 

 Newts, which have a long dentigerous submesial palatine ; the 

 former modification is seen in Amhhjstoma ; but in Sperlepcs and 

 Dcsmognathiis Ave have these two modes combined. The edentulous 

 bone applies itself to the pterygoid process of the suspensorium 

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



In the xinura the pterygo-palatiue cartilages are developed as 

 one, and only become segmented rarely, as in Bufo vulc/aris ; 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 Urodela. 



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 

 types ; it is suppressed in the " Metabola" or Caducibranchs. 



But some of these have pseudo-columella, not lying 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 Menopoma, Spelerpes, and Desmognathus) is of great interest, 

 as showing how Y\ti\e 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 researcli and of 

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



