14 BULLETIN Ml, UNITED STATES NATIONAL MUSEUM. 



Thii ('liariicters display-'d l).v tin? three divisions in question indicate 

 their rehitionship to l)i'. iis Ibllows: The orders of JJivision I ])resent in 

 their cranial structure a greater resembhiuce to the limblinned or 

 cro8soi)ter.> siiHi iishes tlian do either of the others. The third division 

 is the most divergent from tiie t.vi»y, and is in various respects tlie most 

 speciaHzed. This si>ecialization consists not only in a departure from 

 the i)rimitive Batrachia, but also from all other forms of vertebrata. 

 Its specialization is seen in the loss and cocissification of various parts 

 of the skeleton. The ITnulehi display chara(;ters interme<liate between 

 the extremes of the class. Near them the Trachystomata (SirenidaO are 

 still more inferior by loss oi' parts of the skull ami of the pelvic arch. 

 The Prnteida have lost the maxillary arch of the Stegocei)haIi, but re- 

 tain their OS iiitercalare. 



IMIVLOGENV. 



The class IJatrachia holds an imi)()rtant position in the history of the 

 vertebrata, as tlie first meudter of that kin;;dom which occupied the 

 land on the advent of the conditions suitable for air-i)reatbiny types. 

 It thus stands in ance.stral relation to the lines of the Sauropsida and 

 ^lammalia, and as the immediate descendants of the fishes. As rej^ards 

 the extinct orders, the primitive type is evidently the (ranocephala. 

 whose vertebral column displays an arrest of (diaracters which are 

 transitional in the hij^aer vertebrata. From this group the orders 

 ithachitomi, Fauboloi'ieri,and Ste.nocephali have been evidently derived. 

 We may then present the followinj,' fjenealogical table of the class 

 liatrachia : 



Salieutia. 



Tracbystoinata. 



Embolonieri. 



Rhachitomi. 



Ganocephala. 



I 



I 



/ 



N 



1 



