180 



AMPHIBIA. 



chord was persistent, and simply had rings of osseous matter 



deposited in it. 



The points in which the Laby- 

 rinthodonts differ from the modern 

 Uroclela are chiefly to be found 

 in the fact that the head is de- 

 fended by an external covering or 

 helmet of hard and polished osse- 

 ous plates, in the possession of 

 ventral integumentary scutes, in 

 the existence of exoskeletal plates 

 occupying the place of the inter- 

 clavicle and clavicles, in the am- 

 phicoelous form of the dorsal ver- 

 tebrae, and in the complicated 

 structure of the teeth. These 



Fig. 541.— FiMiti. lints of a LabyriiitlKxloiit (( 7,, /,■,,//,, //cw), from the Trias. Tlie uiipor 

 figure sliows a single footprint enlarged ; the lower figure shows a slab, with se\eral jirints, 

 and traversed by reticulated desiccation-cracks. 



