Page 376 - My FlipBook

386 DENTAL ANATOMY.
A fair example of a pleurodont lacertilian is afforded by the majority
of the numerous species of the Iguanidce, although some of the members
of the iguanian family, such as Isturus, Lophyrus, Calotes, and others,
are acrodont. In the horned iguana [Metopocerus coniutus) the max-
illary and premaxillary teeth are from twenty-two to twenty-three in
number upon either side. The central ones of the premaxillary set,
of which there are four, are smallest, the outer ones sHghtly enlarged.
These, together with the first five or six maxillary teeth, have sub-
conic recurved crowns, while the crowns of the posterior maxillary
series are laterally compressed into anterior and posterior cutting
edges and terminated by a principal cusp. Of the two edges, the
anterior is the longer and is interrupted by three minor cusps, the
posterior being shorter and bearing only a single accessory cusji. The
presence of these cusps gives the crown a serrated appearance when
viewed from the side.
The teeth of the lower jaw are from t^vcnty to twenty-two in number
upon either side, and are similar in form to those above, with the excep-
tion that there are generally two accessory cusps upon either trenchant
edge of the crown. There is in addition to these a single row of small
conical teeth supported by each pterygoid bone ; the number of these
varies from five to seven.
The only lacertilian which is known to be poisonous is the " Gila
monster " [Heloderma susjjcchnn) of our American fauna. Recent
experiments of Drs. Mitchell and Reichart of Philadelphia have
demonstrated beyond doubt the poisonous qualities of its salivary
secretion. Considerable interest therefore attaches to its dental organs,
as well as to the anatomy of the poison-glands ; this latter subject I
am, unfortunately, not in a position to describe, and will therefore
limit what I have to say here to a consideration of the teeth only.
This animal, of which there are two species, is confined to the desert
wastes of the South-western United States, where it is not of rare occur-
rence. In life it has a rather repugnant appearance, which is no doubt
increased by our knowledge of its poisonous qualities. It attains a
length of eighteen inches or two feet, and is covered with bright yellow
spots, a circumstance Avhieh gives the name Hdodcrma to the genus,
meaning " sun skin." Its venomous nature was not known until the
exjjeriments above mentioned w^ere made, although Prof. Cope had
reason to stispect as much, and gave the name '^ suspectum " to the
species, which he described several years before.
The teeth are sup]iortcd l)y the premaxillary, maxillary, and dentary
bones, the ])alatine and pterygoids being edentulous. Those of the pre-
maxillary, of which there arc three upon each side, are the smallest of
the upper teeth. They increase regularly in size from before backward,
and form a continuous series, with the maxillary teeth behind, which
continue to augment their dimensions up to the eighth tooth from the
median premaxillary pair or the fifth of the maxillary set. From this
]ioint backward the two remaining teeth l)ecome slightlv smaller. The
teeth of the lower jaw are nine in numlier, and are disposed verv much
in the same manner as those above—the smallest in front and the
largest toward the back part of the mouth. A considerable disparity