208 PALEONTOLOGY. 





Ophidians ; a third group, as the newts and salamanders, 

 represent the Lacertians ; and among the perennibranchiate 

 reptiles there are species {Siren) which combine with external 

 gills the mutilated condition of the apodal fishes. 



Thus it will be perceived that, even if the entire skeleton 



of a Labyrinthodont had been 

 obtained, there is no fixed or 

 characteristic general outward 

 form in the existing Batrachian 

 order whereby its affinity to 

 that group could have been de- 

 termined. The common cha- 

 racters by which the Batra- 

 chians, so diversified in other 

 respects, are naturally asso- 

 ciated into one group or sub- 

 _ class of reptiles, besides being 



Cranium and upper jaw and teeth of 



the Menopome (Menopoma taken from developmental phe- 



alleqhanniense). t n n • i , 



nomena, and from the circulat- 

 ing, generative, and other perishable organs, are manifested 

 in modifications of the skeleton, and principally in the skull. 

 This is joined to the atlas by the medium of two tubercles 

 (fig. 85, d, d) 9 developed exclusively from the ex-occipitals ; 

 the bony palate is formed chiefly by two broad and flat 

 bones (ib. c), called "vomerine," and generally supporting 

 teeth. It is only in the Batrachians among existing reptiles 

 that examples are found of two or more rows of teeth on the 

 same bone, especially on the lower jaw (Ccecilia, Siren). 

 Vertebral characters are here of less value. Some Batrachians 

 have the vertebrae united by ball-and-socket joints, with the 

 cup behind (Pipa), or in front (Rana), as in most recent rep- 

 tiles ; others have biconcave vertebral joints, as in a few recent 

 and most extinct Saurians. Some species have ribs, others want 

 those appendages; the possession of ribs, therefore, even if 



