180 NUMBER. SITUATION.
holding, but not for dividing or masticating their food. The Siren
alone combines true teeth with a horny maxillary trenchant sheath
like that of the Chelonian reptiles.
68. Number.—In no reptile are the teeth reduced to so small a
number as in certain mammals and fishes, nor are they ever so
numerous as in many of the latter class. Some species of Monitor
(Varanus) with sixteen teeth in the upper and fourteen in the lower
jaw, aflord examples of the smallest number in the present class, and
certain Batrachians, with teeth ‘ en cardes’ at the roof of the mouth,
or which have upwards of eighty teeth in each lateral maxillary
series, present the largest number. It is rarely that the number of
teeth is fixed and determinate in any reptile so as to be characteristic
of the species.
69. Situation.—The teeth may be present on the jaws only, as
in the Crocodiles and many Lizards ; or upon the jaws, and roof of
the mouth, and here either upon the pterygoid hones as in the
Iguana and Mosasaur, or upon both palatine and pterygoid hones
as in most serpents, or upon the vomer as in most Batrachia, or
upon both vomerine and pterygoid bones, as in the Axolotl, or
upon the vomerine and sphenoid hones, as in the Salamandra gluti-
nosa, Maclure. With respect to the marginal or jaw-teeth, these
may be absent in the intermaxillary bones, as in many serpents;
or they may be present in the upper and not on the lower jaw, as in
most frogs ; or in both upper and lower jaws, as in the tailed Batrachians
; and among these they may be supported, upon the lower jaw,
by the premandibular or dentary piece as in the Salamanders, Meno-
pome, Amphiume, Proteus; or upon the opercular piece, as in the
Siren ; or upon both opercular and premandibular bones as in the
Axolotl. The palatine and pterygoid teeth may, in the Batrachians,
be arranged in several rows, like the ‘ dents en cardes’ of fishes : the
sphenoid and opercular teeth are always so arranged in the few
species that possess them; .the intermaxillary, maxillary and premandibular
teeth are serial or in one row, with the exception of the
Csecilia and the extinct Labyrinthodon, which have a double row of
teeth at the anterior part of the lower jaw.
70. Form.—The teeth of reptiles, with few exceptions, present a
simple conical form, with the crown more or less curved, and the
apex more or less acute. The cone varies in length and thickness
: its transverse section is sometimes circular, but more commonly
elliptical or oval, and this modification of the cone may be
traced through every gradation, from the thick round tooth of the
Crocodile (PI. 62 a , fig. 9) to the sabre-shaped fang of the Yaranus,
the Megalosaur (ib. fig. 6) and the Cladeiodon (ib. fig. 4). Sometimes,
as in the fully-formed teeth of the Megalosaur, one of the margins of
the compressed crown of the tooth is trenchant, sometimes both are
so ; and these may be simply sharp-edged, as in the Varanus of Timor
or finely serrated, as in the great Varanus (Pl. 68, fig. 3.), the
Megalosaur and the Cladeiodon.
The outer surface of the crown of the tooth is usually smooth ;j
it may be polished, as in the Leiodon (PI. 72, fig. 1), or impressed
with fine lines, as in the Labyrinthodon (PI. 63, 1), or raised into
many narrow ridges as in the Pleiosaur and Polyptychodon (PI. 72,
figs. 3 and 4), or broken by a few broad ridges as in the Iguanodon
(PI. 70, fig. 1), or by a single longitudinal furrow, as in some serpents.
The cone is longest and its. apex sharpest in the Serpents ; from
these may be traced, chiefly in the lizard tribe, a progressive shortening,
expansion of the base and blunting of the summit, of the tooth,
until the cone is reduced to a hemispherical tubercle, or plate, as in
the Thorictes (PI. 66, fig. 6) and Cyclodus (ib. fig. 7).
In the Pleiosaur, (PI. 68, fig. 5), the dental cone is three sided,
with, one of the angles rounded off. The posterior subcompressed
teeth of the alligator present a new modification of form ; here they
terminate in a mammilloid summit, supported by a slightly constricted
neck (PI. 75, fig. 3). In the tooth of the Hykeosaur (PI. 62 a , fig. 8.) the
expanded summit is flattened, bent, and spear-shaped, with the
edges blunted. But the expansion of the crown is greatest in the
subcompressed teeth of the Iguanas (PI. 70, figs. 6 and 7 and
PI. 66, fig. 5), which are further complicated by having the
margins notched. The extinct Iguanodon has the crown of the tooth
expanded both in length and breadth, and combining marginal dentations
with longitudinal ridges, presents the most complicated external