64 BATRACHIAN ILLUSTRATIONS OF THE 



PRINCIPAL FORMS OF THE SKELETON IN THE 

 CLASS REPTILIA. 



The transition from fishes to reptiles is easy, and the 

 signs thereof very manifest in the skeleton. In the 

 thorn-back and allied fishes the skull articulates with 

 the trunk by two condyles, and the part answering to the 

 basioccipital is a depressed plate. The Batrachia^ or low- 

 est order of reptiles — including the siren, proteus, frog, 

 toad — have a similar double articulation of the skull 

 with the trunk, the two condyles being developed from 

 the two exoccipitals. Hsemapophyses are not present as 

 bones in the abdominal part of the trunk of Batracliia^ 

 but they are so developed in the tail. This structure, 

 with the detachment of the scapular arch from the occi- 

 put, and the absence of dermoneural and dermohaemal 

 spines, serves to distinguish the most fish-like batrachian 

 from the protopterus and lepidosiren, which are the 

 most reptile-like of fishes. 



In commencing the study of the skeletons of reptiles 

 in the most fish-like of the class, we find a much less 

 complex condition of the osseous framework of the body 

 than in the bony fishes; this will be immediately mani- 

 fest by a comparison of the skeleton of the menopome 

 (which may be seen in the Museum, Royal College of 

 Surgeons, No. 583), as an example of the perennibran- 

 chiate batrachia, with the skeleton of the trout (No. 45) 

 or of the haddock (No. 176, in the same Museum). 



The diflerence tends greatly to elucidate the true nature 

 of the complexities of the fish's skeleton, since it chiefly 

 consists in the simplification of that of the batrachian, by 

 the non-development of the parts of the dermal skeleton 

 which characterize that of the fish. The suborbital, super- 



