ORDERS OF AMPHIBIA. 391 



which they climb with ease. They are mostly found in warm 

 countries, especially in America, but one species is European 

 (% 146). 



ORDER IV. LABYRINTHODONTIA. The members of this, 

 the last order of the Amphibia, are entirely extinct. They 

 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 Jagaeri) 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. 152). So like were 

 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, however, 

 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. 



Fig. 152. Footprints of a Labyrinthodont (CheirotJieriunl). 



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 (amphiccelous). " 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 was arti- 

 culated to the vertebral column by two occipital condyles. 

 The teeth are rendered complex by numerous foldings of their 



