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TEETH OF THE VERTEBBATA. 383
like reptiles which has been designated the Theromoq^ha by Prof. Cope.
This group includes two important divisions, one of which, tlie Anomo-
dontia, was first described by Prof Owen from the Triassic (?) deposits
of South Africa ; the other is the Felycosauria, which is so far known
only from the American Permian.
The osteological structure of this order furnishes us many transitional
characters between the Batrachia and more typical Reptilia, on tlie one
hand, while on the other they seem to stand in ancestral relationship to
the prototherian Mammalia. Their batrachian affinities are manifested
in the structure of the pectoral and pelvic arches, in the structure of the
limbs, and the possession of teeth on the vomer. In the absence of a
parasphenoid bone in the base of the cranium and the unicondylian
condition of the skull they are markedly reptilian. The structure
of the pelvic and pectoral arches and limbs, together with the intercen-
tral articulation of the ribs, allies them with the lower Mammalia.
Their dental organs present a considerable variety of structure—in
some instances departing widely from the simple conical form usual
among the other orders of this class of the Vertebrata. In one genus
(iJimetrodon) there were two large caniniform teeth in each premaxil-
lary, implanted in distinct sockets ; these were followed by a single row
of maxillary teeth, whose crowns resemble somewhat the premolars
of the dog in general pattern. They were lodged in distinct alveoli,
and exhibit the remarkable peculiarity of being implanted by double
fangs, or rather single ones deeply grooved upon either side, otherwise
unknown among the Peptilia. The first tooth behind the maxillo-pre-
maxillary suture is enlarged into a canine, and the entire maxillary
series does not exceed fifteen in number. The palato-pterygoid arch is
present, and one of its elements, probably the pterygoid, is thickly
studded with small conical teeth irregularly disposed. Another element
which lies internal to this last-mentioned bone is described by Prof.
Cope as bearing a single row of teeth. Other genera related to this
one are.Theroplewa, Clepsydrops, etc. of Cope, Avhich present minor
differences in the form and size of the corresponding teeth.
A nearly-allied family of this group is the Diadcdidm, likewise
described by Cope. A typical example of the dentition of this family
is seen in Empedodes molaris, wherein the pattern of the crowns of the
molars is thoroughly unique. The teeth are disposed on the borders of
the premaxillary, maxillary, and dentary bones, as well as upon the
vomer, which forms a median keel in the roof of the mouth. The max-
illo-premaxillary set in the upper jaw describe a sigmoid curve in their
line of implantation, and form an uninterrupted series from the front
to the back of the mouth. There are fourteen teeth belonging to this
series, of which the first two are larger than those immediately succeed-
ing them. They have obtuse subconic croAvns, and are lodged in dis-
tinct alveoli. From this point the teeth gradually decrease in size up
to the sixth, when they again become larger and more complex in pat-
tern. The crowns of the typical molars have a much greater transverse
than longitudinal extent ; "the grinding surface is somewhat elliptical in
outline, and is provided with a submedian cusp which stands nearer the
outer than the inner border. The portion of the crown external and