390 
division of the skull was broad, much depressed and flattened, re- 
sembling the skull of the gigantic Salamander and of the Alligator ; 
and the outer surface of the bones was strongly sculptured, as in the 
Crocodilian family, but of a relatively larger and coarser pattern. 
The fragment described contains the anterior moiety of the single 
row of small teeth, or 30 sockets, and the base of one of the great 
anterior tusks. The bases of the serial teeth project directly from 
the outer wall of the shallow socket, there being no alveolar ridge 
external to it. The large anterior fang is three times the size of the 
first of the serial teeth, and the size of these gradually diminish as 
they are placed further back ; the length of the common-sized being 
about two lines, and the greatest breadth one-third of a line. The 
apical two-thirds of each tooth is smooth, but the basal third is fluted, 
and anchylosed to the outer wall of the socket. The breadth of the 
upper jaw, opposite the middle of the dental series, was two inches 
six lines; in proceeding backwards the jaw gradually expands to 
three inches, and in proceeding forwards narrows, but in a less 
degree towards the anterior extremity, and then slightly widens or 
inclines outwards on account of the large tusks. Where the upper 
jaw is entire, a portion next the median suture, four lines in breadth, 
is separated from the maxillary bone by a longitudinal harmonia, 
and corresponds with the position of the nasal bone in the Crocodile. 
On comparing the structure of the cranium of the Labyrinthodon 
with the Batrachian condition of the same part, Mr. Owen shows ~ 
that an important difference will be found to exist. In both the 
ccaducibranchiate and perennibranchiate species, the upper maxillary 
bones do not extend horizontally over the upper surface of the skull, 
but leave a very wide interval between the maxillary and nasal 
bones ; and the palatal processes of the former contribute as little to 
form the floor of the nasal cavity: in the Crocodiles, on the contrary, 
the palatal processes of the maxillary bones extend horizontally in- 
wards, and meet at the middle line of the roof, forming an unbroken 
floor to the nasal cavity. In the Labyrinthodon the superior max~ 
illary bones, as already shown, extend inwards to the nasal bone, 
constituting with it a continuous roof to the nasal cavities ; but the 
palatal processes, instead of reaching to the middle line, as in the 
Crocodiles, are very narrow, as in the Batrachia. The osseous roof 
of the mouth is principally composed of ‘a pair of broad and flat 
bones, analogous to the divided vomer in Batrachia, but of much 
greater relative extent, approaching, in this respect, those of the 
Menopome, and defending the mouth with a more extensive roof of 
bone than exists in any Lacertian reptile : ‘* physiologically, there- 
fore,’ observes Mr. Owen, ‘‘the Labyrinthodon, in this part of its 
structure, comes nearest to the Crocodile; but the structure’ itself; 
morphologically, is essentially Batrachian.” In the Menopome and 
gigantic Salamander, a row of small teeth extends transversely 
across the anterior extremity of the vomerine bones: and the occur- 
rence in the Labyrinthodon of a similar row, consisting in each 
palatine bone of three median small teeth and two outer larger ones, 
marks most strongly its Batrachian nature; and from the outer- 
