AMPHIBIA. 179 



pair being much larger tlian the one in front (fig. 541). So 

 like were these impressions to the shape of the human hand, 

 that the unknown animal which produced them was at once 

 christened Cheir other ium, or " Hand-beast." Further dis- 

 coveries, however, soon showed that the footprints of Cheiro- 

 tlierium had been produced by different species of Batra- 

 chians, to which the name of Labyrinthodonts was applied 

 in consequence of the complex microscopic structure of the 

 teeth. 



The order Labyrintliodontia is thus defined by Professor 

 Huxley : " The body is salamandriform, with relatively weak 

 limbs and a long tail. The dorsal vertebrae, when completely 

 ossified, are biconcave, with double transverse processes. The 

 ribs have distinct capitula and tubercula. 



" In the thoracic region, three superficially sculptured exo- 

 skeletal plates, one median and two lateral, occupy the place 

 of the intercla^dcle and clavicles. Between 

 these and the pelvis is a peculiar armour, 

 formed of rows of oval dermal plates (fig. 

 540), which lie on each side of the middle 

 line of tlie abdomen, and are directed ob- 

 liquely forwards and inwards, to meet in 

 that line. 



" The skull has distinctly ossified epi- 

 otic bones, in the same position and of -o- ... ^ 



' ^ Fig. 540.— One of the 



the same form as those of fishes. The mtegumentary scutes of 



. - ^ - - Anthracosauriis Russelli, 



cranial bones are sculptured, and many ex- one-haif of the natural 

 hibit peculiar smooth symmetrical grooves (2ter AttheV-f^''''^''' 

 — the so-called ' mucous canals.' 



" The parietes of the teeth are deeply plaited and folded, 

 so as to give rise to a complicated ' labyrintliine ' pattern in 

 the transverse section of the tooth." 



There appear usually to have been both pairs of limbs 

 developed, but some forms which have been referred here 

 (such as Ophider'peton) possessed a serpentiform body, and seem 

 to have been apodal. Little is known, necessarily, of their 

 development, but the singular genus Archegosmirus possessed 

 permanent branchial arches, and was, therefore, apparently 

 perennibranchiate (if not truly a larval form), whilst its noto- 



