THE BATRACHIA OF NORTH AMERICA. 13 



CLASSIFICATION. 



There are several orders of Batrachia, aud they display remarkable 

 diversities of skeletal structure. For the better understanding of these 

 I give the following table of their principal definitions :i 



I. Basioccipital, supraoccipital, intercalary,'^ and supratemporal bones present. Pro- 



podial bones distinct. 

 a. One cotyloid occipital condyle. 



Vertebral centra replaced by one basal and two lateral elements 



with one neural arch Ganocephala. 



aa. Two occipital condyles. 



Vertebral bodies, including atlas, segmented, one set of segments 



together supporting one arch Ehachitomi. 



Vertebrse segmented, the superior and inferior segments each 



complete, forming two centra to each arch Emholomerl. 



Vertebral bodies, including atlas, not segmented ; one to each 

 arch Stegocephali. 



II. Basioccipital, snpraoccipital, and supratemporal bones wanting. Frontal and 



propodial bones distinct. 

 a. An OS intercalare. 



A palatine arch and separate caudal vertebrae Proteida. 



aa. No OS intercalare. 



A maxillary arch and vomers ; palatine arch present, imperfect ; 



nasals, premasillaries and caudal vertebrae distinct Urodela. 



No maxillary or palatine arches; no vomers; nasals and pre- 

 maxillary, also caudal vertebrae, distinct Trachystomata. 



III. Basioccipital, supraoccipital, intercalare, and supratemporal bones wanting* 



Frontals and parietals connate; propodial bones and lumbosacral vertebrae 

 each confluent. 

 Palatines distinct from vomers ; a palatine arch ; astragalus and 



calcaneum elongate, forming a distinct segment of the limb Salientia. 



The animals of the Division I are all extinct. Division II includes the 

 Salamanders and their allies, with tbe worm-like Coecilians (Apoda), 

 while the third division embraces the frogs, toads, etc. 



AFFINITIES. 



The Batrachia are, then, intermediate in characters, and therefore in 

 position, between the fish-like forms aud the reptiles. Among the 

 former the Dipnoi approach them most nearly, while the extinct reptiles 

 of the oldest order, the Theromora,^ are the nearest allies on the rep- 

 tilian side. It belongs to the series of vertebrates which have a dis- 

 tinct coracoid bone in the shoulder-girdle, and a distinct quadrate bone 

 in the skull. The greater part of the basicranial axis is cartilaginous, 

 but it is protected below by the membrane bone, the parasphenoid. In 

 all these respects, and in the absence of an amnion of the embryo, the 

 Batrachia agree with the fishes. They difterfrom this class in tbe pres- 

 ence of legs and absence of fins, and in the absence of various bones 

 ■which belong to the branchial and opercular systems, and to the sus- 

 pensor of the lower jaw. 



^This is partly derived from the table which I have given in Vol. II, Palaeontology 

 of the Geological Survey of Ohio, 1874, p. 352. See also American Naturalist, 1884. 

 ^Of Cuvier : Ej)iotic of Huxley, according to Vrolik. 

 *TAerowiorj)/ia Cope'olim; name preoccupied. 



