The portion of the superior maxillary bone contains the anterior
part of the single row of small teeth, and the base of one of the great
anterior tusks, which ranges in the same line with the other teeth,
but is directed obliquely backwards; the small serial teeth project
more vertically from the alveolar margin of the jaws and
are slightly inclined outwards. In a few places the contiguous
teeth are present, hut throughout the greater part of the series there
is alternately a tooth and an empty socket. The sockets are shallow,
and are so closely arranged, that, although the alveolar series in the
present fragments is hut two inches, three lines in extent, it contains
thirty-one sockets. The large anterior fang is three times
the size of the first of the serial teeth which succeeds it; and the rest
gradually diminish as they recede backwards, so that the eighth tooth,
counting the sockets from the first, is little more than half a line in
diameter at its base ; beyond this the teeth are of equal size. Each
of the serial teeth is slender in proportion to its length, and gradually
diminishes from the middle of the crown to the apex, which is not
very acute where entire; a linear pulp-cavity is continued along the
centre of the tooth nearly to the apex. The transverse section of
the base is elliptical, its smallest diameter being in the axis of the
jaw; that of the apical two thirds of the tooth is circular ; the basal
third is finely fluted, the rest of the tooth is smooth. The outer wall
of the socket is very thin, and is confluent with the fluted base of
the tooth. From the flatness and thinness of the maxillary hones, the
sockets of the teeth are necessarily shallow. The length of the common
sized serial teeth is about two lines, their greatest diameter one
third of a line; the diameter of the base of the large anterior tusk
is two lines and a half.
The whole of the under surface of the fossil was covered by the
sandstone matrix, but the fractured margin, opposite the alveolar
border, exhibited the edge of a thin plate of bone, uninterrupted in
the longitudinal extent, and forming the floor of a wide and shallow
nasal cavity, thus affording a strong indication that the Labyrinthodon
breathed air like the higher reptiles. That the bony palate extended
as far in the transverse as in the longitudinal extent was indicated
by the projecting base of a fractured conical tooth, twice the size
of the large anterior fang of the maxillary series, and situated
internal to the anterior small serial teeth. The crocodilian affinities
of the Labyrinthodon we have just seen to have been manifested in
the character of the bones forming the upper surface of the maxillary
part of the cranium, and by the interception of a wide and shallow
nasal- cavity between two horizontal plates of bone. The main test
of the value of this manifestation would be the actual condition of the
bony palate, first in regard to the bones composing it, and secondly
in relation to the dental system. In Crocodiles the floor of the nasal
cavity is chiefly formed by the maxillary bones, in Batrachians by
the divided and expanded vomer ; in all Crocodiles the bones of the
palate are edentulous, in most Batrachians they support teeth. There
was evidence in the fossil in question of a large laniary tooth projecting
from the palatal surface of the mouth, internal to the series of maxillary
teeth ; it remained to be determined whether this was supported
upon the same bone which supported the serial teeth, viz. the superior
maxillary, or whether it was a true palatal or vomerine tooth. A
careful removal of the adherent matrix brought to light this very
instructive part of the cranial anatomy of the Labyrinthodon, (PI.
63 a , fig. 3). The palatal processes of the maxillary bones instead
of extending to the middle line, as in the Crocodiles, are very
narrow, as in the Batrachians. The osseous roof of the mouth is
principally constituted by a pair of broad and flat bones analogous
to those which Cuvier describes as a divided vomer in the Batrachians.
These bones are, however, of greater relative extent than
in any existing Batrachians; they defend the mouth with a more
complete bony roof than is present in most Lacertian reptiles.
Physiologically the Labyrinthodon in this part of its structure
comes nearest to the crocodile, but the structure itself, morphologically,
is essentially Batrachian; that is to say, the bony palate is
formed by largely developed vomerine bones, situated, as in the
Batrachians, at a part of the skull which is occupied solely by the
maxillary bones in the crocodiles.
The divided vomer varies much in form in the Batrachians ; that
of the Menopome most resembles the vomer of the Labyrinthodon
in its broad anterior extremity, and the large tooth (fig. 3, c) is