BATRACHIA. 



319 



in two points instead of one. This is the family of toads, or Bufoniila;. Several fami- 

 lies have teeth and embryonic shoulder girdle. The family which has teeth and firnii- 

 sternal suoulder-girdle is the RanidiB, or true frogs. Now the frogs 

 of each of these divisions present nearly similar scales of development 

 of another part of the skeleton, viz. : the bones of the top of the skull. 

 We find some in which the front one of these bones (ethmoid) is 

 represented by cartilage only, and the middle ones, or fronto-jiarietals 

 and the nasals, are represented by only a narrow striji of bone each. 

 In the next type the ethmoid is ossified ; in the next, we have the fio. isgl^iermini 

 fronto-parietal completely ossified. The nasals may range from ftrooSf- araferous 

 narrow strips to complete roofs. In the fourth station on the line, ^^^^' 

 these bones are I'ough, with a hyperostosis of their surfaces ; and in the next 

 set of sjiecies, this ossification fills the skin, which is thus no longer separable from the 

 cranial Iwnes; in the sixth form the ossification is ex- 

 tended so as to roof in the temporal muscles and enclose 

 the orbits behind ; while in the rare seventh and last 

 stage, the tympanum is also enclosed behind by Ivone. 

 Now all of these types are not found in all of the families 

 of the Anura, but the greater number of them are. Six 

 principal families, five of which belong to the Arcifera, 

 are named in the diagram below, and three or four 

 others might have been added. I do not give the 

 names of the genera which are defined as above de- 

 scribed, referring to the explanation of the cuts for 

 them, but indicate them by the numbers on the left margin of the page, which 

 correspond to those of the definitions above given. A zero mark signifies the absence 

 or nou-discovery of a generic type. See pp. 320, 321. 



Sternum embryonic. Sternum complete. 



Arcifera. Firmistemia. 



Fig. 189. — sternum of liana tempo 

 raria ; tirmistenious type. 



It is evident, from what has jireceded, that a perfecting of the shoulder-girdi 

 any of the species of the Areiferous columns would 

 place it in the series of Firmisternia. An accession of 

 teeth in a species of the division Bufonidaj would 

 make it one of the Scaphiopidaj ; while a small amount 

 of change in the ossification of the bones of the skull 

 would transfer a species from one to another of the 

 generic stations represented by the numbers of the columns from one to seven. 

 There are few groups where this law of jiarallelism is so readily observed amouti 



'Ki. 190. — Ster 

 liana titnporai 

 just budding. 



