350 AMPHIBIA. 



anchylosed to form single bones (fig. 308). The mouth is 

 sometimes edentulous, but the upper jaw has usually small 

 teeth, and the lower jaw sometimes. The hind-limbs usually 

 have the digits webbed for swimming, and are generally much 

 larger and longer than the fore-limbs. 



The geological history of the Anoura, as in the case of the 

 Urodela, is of small importance. The two chief groups of the 

 living A?wura namely, the Frogs and the Toads are both 

 represented in past time ; but they do not appear to have come 

 into existence till after the commencement of the Tertiary 

 period. Most of the fossil forms have been detected in de- 

 posits of Miocene age. 



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 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. 309). 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 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 order Labyrinthodontia 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 ckpitula and tubercula. 



" In the thoracic region, three superficially sculptured exo- 

 skeletal 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 forwards and inwards, to meet in that line. 



"The skull has distinctly ossified epiotic bones, in the same 

 position and of the same form as those of fishes. The cranial 

 bones are sculptured, and many exhibit peculiar smooth sym- 

 metrical grooves the so-called ' mucous canals.' 



