CHAPTER XII. 



GENERAL ACCOUNT OF THE SKELETON IN 

 AMPHIBIA. 



EXOSKELETON. 



The exoskeleton, at any rate in most living forms, is very 

 slightly developed in Amphibia. The only representatives 

 of the epidermal exoskeleton are (1) the minute horny beaks 

 found coating the premaxillae and dentaries in Siren and the 

 tadpoles of most Anura, (2) the nails borne by the first three 

 digits of the pes in Xenopus and by the Japanese Salamander 

 Onychodactylus, (3) the horny covering of the calcar or pre- 

 hallux of frogs. The Urodela and nearly all the Anura, which 

 form the vast majority of living Amphibia, have naked skins. 

 A few Anura belonging to the genera Ceratophrys and Brachy- 

 cephalus have bony dermal plates developed in the skin of the 

 back, and these plates become united with some of the under- 

 lying vertebrae. 



In the Gymnophiona the integument bears small cycloid 

 scales arranged in rings which are equal in number to the 

 vertebrae. These scales contain calcareous concretions. Scales 

 also occur between the successive rings. 



In the Labyrinthodontia the dermal exoskeleton is in 

 many genera greatly developed. It is generally limited to the 

 ventral surface and consists principally of a buckler formed 

 of three bony plates, one median and two lateral. These 



