VERTEBRATA: AMPHIBIA. 523 



were Batrachians, probably most nearly allied to the Urodela, 

 but all of large size, and some of gigantic dimensions, the skull 

 of one species (Labyrinthodon Jcegeri] being upwards of three 

 feet in length and two feet in breadth. The Labyrinthodonts 

 were first known to science simply by their footprints, which 

 were found in certain sandstones of the age of the Trias. 

 These footprints consisted of a series of alternate pairs of 

 hand-shaped impressions, the hinder print of each pair being 

 much larger than the one in front (fig. 285). So like were 



Fig. 285. Footprints of a Labyrinthodont (Cheirotherium). 



these impressions to the shape of the human hand, that the 

 unknown animal which produced them was at once christened 

 Cheirotherium, or " Hand-beast." Further discoveries, how- 

 ever soon showed that the footprints of Cheirotherium had 

 been produced by different species of Batrachians, to which 

 the name of Labyrinthodonts was applied, in consequence of 

 the complex microscopic structure of the teeth. 



The Labyrinthodonts were " salamandriform, with relatively 

 weak limbs and a long tail" (Huxley). The vertebral centra 

 and arches were ossified, and the bodies of the dorsal vertebrae 

 are biconcave (amphicoelous). " In the thoracic region three 

 superficially sculptured exoskeletal plates, one median and two 

 lateral, occupy the place of the interclavicle and clavicles, 

 Between these and the pelvis is a peculiar armour, formed 

 of rows of oval dermal plates, which lie on each side of the 

 middle line of the abdomen, and are directed obliquely for- 

 wards and inwards to meet in that line " (Huxley). 



The head was defended by an external covering or helmet 

 of hard and -polished osseous plates, sculptured on their exter- 

 nal surface, and often exhibiting peculiar, smooth, symmetrical 

 grooves the so-called "mucous canals." The skull (fig. 287) 

 was articulated to the vertebral column by two occipital con- 

 dyles. The teeth (fig. 286) are rendered complex by numer- 

 ous foldings of their parietes, giving rise to the "labyrinthine" 

 pattern, from which the name of the order is derived. 



There appear usually to have been both pairs of limbs de- 

 veloped, but some forms which have been referred here (such 

 as Ophiderpeton} possessed a serpentiform body, and seem to 



