From the study of the living
_Ceratodus_, it is certain that the genus belongs to the same
group as the existing Mud-fishes (_Dipnoi_); and we therefore
learn that this, the highest, group of the entire class of Fishes
existed in Triassic times under forms little or not at all different
from species now alive; whilst it has become probable that the
order can be traced back into the Devonian period.
[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 Wuerttemberg.]
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.
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