PHYLOGENY. 113 



and persistent gills of the Protei'da ; the absence of 

 the maxillary bones and the presence of gills in the 

 Trachystomata ; the loss of a pair of legs and feeble- 

 ness of the remaining pair in the same ; and the ex- 

 treme reduction of the limbs in Amphiuma, and their 

 total loss in the Caeciliidae. Such I must also regard, 

 with Lankester, the persistent branchiae of the sire- 

 dons. I may add that in the brain of the protei'd Nec- 

 turus the hemispheres are relatively larger than in the 

 Anura, which are at the end of the line. 



It must be concluded, then, that in many respects 

 the Batrachia have undergone degeneracy with the 

 passage of time. 



d. The Reptilian Line. 



As in the case of the Batrachia, the easiest way of 

 obtaining a general view of the history of this class is 

 by throwing their principal structural characters into a 

 tabular form. As in the case of that class, I commence 

 with the oldest forms and end with the latest in the 

 order of time, which, as usual, corresponds, with the 

 order of structure. I except from this the first order, 

 the Ichthyopterygia, which we do not know prior to 

 the Triassic period : 



I. The quadrate bone united with the adjacent elements by suture. 

 A. Temporal region of skull with a bony roof ; no postorbital 

 bars. 



Supramastoid bone present ; an interclavicle ; limbs 



ambulatory ; Cotylosauria. 



AA. Cranium with one postorbital bar ; no sternum. (Sy- 



naptosauria.) 

 a. Paroccipital bone distinct. 



A supramastoid bone ; ribs two-headed on centrum ; 

 carpals and tarsals not distinct in form from meta- 

 podials ; Ichthyopterygia. 



