LABYrUNTIIODONTIA 



185 



deposit, were trodden by reptiles having the essential bony 

 characters of the modern Batvachia, but combining these with 

 other bony characters of crocodiles, lizards, and ganoid fishes ; 

 and exhibiting all under a bulk which, as made manifest by 

 the fossils and footprints, rivalled that of the largest crocodiles 

 of the present day. The form of the largest Labyrinthodonts, 

 if we may judge by the great breadth and flatness of the skull, 

 and the proportions of certain bones, seems to have been 

 something between that of the toad or land-salamander. 



The smooth-skinned Batrachians have no fixed type of exter- 

 nal form like the existing higher orders of reptiles, but some, as 

 the broad and flat-bodied toads and frogs, most resemble the 

 Chelonians, especially the soft-skinned mud-tortoises {Trionyx); 

 other Batrachians, as the Ccecilicc, resemble Ophidians ; a third 

 group, as the newts and salamanders, represent the Lacertians ; 

 and among the perennibrauchiate reptiles there are species 

 (Siren) which combine with external gills the mutilated con- 

 dition 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 Batrachian order 

 whereby its affinity to that group 

 could have been determined. 

 The common characters by 

 which the Batrachians, so di- ( "^ 

 versified in other respects, are y 

 naturally associated into one 

 group or sub-class of reptiles, 

 besides being taken from the 

 condition of the circulating and 

 generative systems, and other 

 perishable parts, are manifested in modifications of the skeleton, 



Fig. 65 a. 



Cranium and upper jaw and teeth of 



the Menopnme (Menopoma 



alleghanniense). 



