I 



THE BATliACHlA OF NUKTII AMERICA. 



15 



As regards the connection of the class, as a whole, with other classes 

 of vertebrata, it 's very probable that the extinct orders, as the Gano- 

 ceiihala, were denveri ♦roiu some extinct form of Dipnoau fishes, more 

 or less related to the group of which the genus Ceratodus is a represent- 

 ative. In this type we have a persistent chorda dorsalis, fins which 

 present the type from which ambulatory limbs were derived, a pelvis, 

 and a cranium nearer that of the batrachians than most other fishes 

 pre.-^ent. The Crossopterygia are a little on one side of the parental 

 stem, since they have no pelvi.^*, and their limbs begin to show a begin- 

 ning of that reduction and specialization which is carried to such an 

 extent in the Actinopterygia, or typical H.shes. 



From the Ganocepiiala we derive the remaining orders, all of which 

 possess two occipital condyles. The intercentra, which are small in tlie 

 prepel vie vertebral axis of the Ganocephala, assume a large development 

 in the Embolomeri, wbich thus have two bodies to each neural arch 

 throughout the series. It is probable that the reptiles took their origin 

 from this grouj) by the gradual reduction of the intercentra, and the 

 continued dominance of the centra. It is possible also that the Em- 

 bdloi eri possess but one occipital condyle, which, uniting with an in- 

 tercentrum, formed the single occipital condyle of the Reptilia. 



In the direction of the lihachitomi there is reason to believe that the 

 intercentra became predominant in the vertebral axis, and that th^ 

 centra soon disappeared. This order gave origin to the Stegocephala, 

 in which the centra are wanting; and this order was the .source of the 

 Proteida on one hand, and the Salientia on the other. The formei', of 

 all the existing orders is the only one which retains the os intercalare 

 of the Pahvozoic types. From the Proteida we get the Urodela, and 

 from the latter the Trachystomata, as will be more especially shown 

 under that order. 



The Ganocephala (Trimerorhachis) and the Rhachitomi (Zatrachys) 

 had a well developed columella auris, which extended from the lieuestra 

 ovale and turned upwards and backwards to the notch of the posterior 

 outline of the skull between the os intercalare and the base of the quad- 

 rate. It is highly probable that this notch was occupied by a tympanic 

 drum.' In the Proteida, Urodela, and Trachystomata, there is no col- 

 umella. In the Salientia there is a chain cousistiug of one bone and 

 two cartilages extending between the stapes and the memhranum tym- 

 imni. Thus the LTrodela in this resi)ect have undergone degeneration, 

 while the Salientia have undergone specialization. With regard to 

 other parts of the skeleton all the later and recent orders must be re- 

 garded as having undergone degeneration, in view of the extensive loss 

 of parts. (See Origin of the Fittest, by E. D. Cope, On the Evolution 

 of the Vertebrata, progressive and retrogressive.) 



'See Cope On tbe ossicula iiuditns of the Batracbia, Aiuer. Naturalist, 1888, p. 464; 

 Journal of Morphology, November, 1?88. 



