[Illustration: Fig. 148.--Footprints of a Labyrinthodont (_Cheirotherium_), from the Triassic Sandstones of Hessberg, near Hildburghausen, Germany, reduced one-eighth. The lower figure shows a slab, with several prints, and traversed by reticulated sun-cracks: the upper figure shows the impression of one of the hind-feet, one-half of the natural size. (After Sickler.)] [Illustration: Fig. 149.--Section of the tooth of _Labryinthodon (Mastodonsaurus) Joegeri_, showing the microscopic structure. Greatly enlarged. Trias.] [Illustration: Fig. 150.--a, Skull of _Labyrinthodon Joegeri_, much reduced in size; b, Tooth of the same. Trias Württemberg.] The _Amphibians_ of the Trias all belong to the old order of the _Labyrinthodonts_, and some of them are remarkable for their gigantic dimensions. They were first known by their footprints, which were found to occur plentifully in the Triassic sandstones of Britain and the continent of Europe, and which consisted of a double series of alternately-placed pairs of hand-shaped impressions, the hinder print of each pair being much larger than the one in front (fig. 148). So like were these impressions to the shape of the human hand, that the at that time unknown animal which produced them was at once christened _Cheirotherium_, or "Hand-beast." Further discoveries, however, soon showed that the footprints of _Cheirotherium_ were really produced by species of Amphibians which, like the existing Frogs, possessed hind-feet of a much larger size than the fore-feet, and to which the name of _Labyrinthodonts_ was applied in consequence of the complex microscopic structure of the teeth (fig. 149). In the essential details of their structure, the Triassic Labyrinthodonts did not differ materially from their predecessors in the Coal-measures and Permian rocks. They possessed the same frog-like skulls (fig. 150), with a lizard-like body, a long tail, and comparatively feeble limbs. The hind-limbs were stronger and longer than the fore-limbs, and the lower surface of the body was protected by an armour of bony plates. Some of the Triassic Labyrinthodonts must have attained dimensions utterly unapproached amongst existing Amphibians, the skull of _Labyrinthodon Joegeri_ (fig. 150) being upwards of three feet in length and two feet in breadth. Restorations of some of these extraordinary creatures have been attempted in the guise of colossal Frogs; but they must in reality have more closely resembled huge Newts.