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388 DENTAL ANAT03IY. :

worn out. One striking peculiarity which this reptile presents is in the
dentigerous character of the splenial and the edentulous condition of
the dentary bones of the mandible. The teeth are relatively small, and
are placed at some distance from the anterior part of the mouth. This
part of the jaws is believed to have been occupied by a kind of horny
sheath similar to that found in birds and turtles.
The proportions of the limbs were those of the kangaroo, the posterior
greatly exceeding the anterior in size. The general shape of the skull
is very much like that of a bird with a large spatulate beak ; it was
supported upon a long, flexible neck, which was doubtless useful to the
animal in gathering the soft aquatic vegetation upon which, from the
character of its teeth, it is supposed to have subsisted. It likewise
had a powerful tail, much deeper than thick, which probably served
not only as a fifth limb in balancing the weight of the animal, but
could also have been useful as a swimming organ. The feet were pro-
vided with true hoofs.
The carnivorous dinosaurs were scarcely inferior in size to the her-
bivorous species, but were of a more slender and active build. Their
jaws were provided with large, powerful conical teeth, better adapted
for the capture of living animal prey. The terminal phalanges were
ensheathed in distinct claws.
Another order of the Reptilia, and one which is probably best known,
is the Ophklia, or snakes. Especial interest attaches itself to the dental
organs of many of this group, inasmuch as their poisonous bite consti-
tutes one of their most conspicuous features and renders them particu-
larly obnoxious as well as dangerous to life.
According to most systematists, the order is divisible into five sub-
orders, which have been defined as follows
I. " The palatine bones widely separated, and their long axes longitudinal ; a trans-
verse (ecto-pterygoid) bone; the pterygoids unite with the quadrate bones."
" None of the maxillary teeth grooved or canaliculated " Asinca.
n.
b. " Some of the ])osterior maxillary teeth grooved " Torfriciiia.
c. "Grooved anterior maxillary teeth succeeded by solid teeth" . Proteroglyphia.
d. "Maxillary teeth few, canaliculated, and fang-like" Solenofilyphin.
II. "The jialatine bones meet or nearly meet in the base of the skull, and their long
axes are transverse. No ecto-pterygoid bone ; the jiterygoids are not con-
nected with the quadrate bones" (Huxley) . .* Scalecophidia.
""The first of these sub-orders includes nearly all of the harmless or non-
venomous species, of which the black snake, garter snake, boa, etc. are
familiar examples. The second includes a single family with few species,
said to be harmless ; they are confined to Africa. The third sub-order
embraces such forms as the deadly cobra, the coral snake, harlequin
snake, and others. The fourth includes the vipers, rattlesnakes, adders,
etc. The last is represented by few species which are non-venomous.
In general, the dentigerous elements of the ophidian skull may be said
to consist of maxillary, jxilatine, and jiterygoid bones of the upper and
the dentary bones of the loNver jaw, although in the pythons and tor-
trices teeth exist upon the premaxillaries as Avell. In JRachiodon, a
singular African species of the Asinea, the teeth of the jaws are
extremely small and soon disappear. This loiss is compensated for by
an excessive development of the hypopophyses of several of the anterior