224 Animal Life 
insects. These teeth, 1t may be added, are welded 
to the inner side of the raised outer parapet of 
the jaws, smaller teeth being present on some of 
the bones of the palate. 
Herbivorous lizards are almost unknown save 
in the tropical portions of the New World, where 
- they are represented by the numerous tribe of 
Iguanas, many of which attain bodily dimensions 
exceeded only by the monitors of the Hastern 
Hemisphere. In the more typical representatives 
of these lizards (Fig. 7) the front teeth are simple 
cones, but those on the sides of the jaws have 
laterally-compressed crowns and saw-like edges, 
those of the upper and lower jaws working against one another in a manner admirably 
calculated to masticate food. In the two remarkable iguanas inhabiting the Galapagos 
Islands, one of which is largely marine, while the other is exclusively terrestrial, all 
the teeth are laterally flattened, with their crowns surmounted by three small cusps. 
Very noteworthy is the dentition of the two beautifully-coloured species of poisonous 
lizards (Heloderma) from Central America, Mexico, and Arizona, one of which is 
commonly known as the Gila Monster. These lizards eject poison into the wounds 
made by their teeth in the same manner as venomous serpents, and their dentition 
corresponds very closely with that of the latter. The curved and fang-like teeth, 
which are very loosely attached to the jaws, are provided 
with grooves for the transmission of the venom, which, as 
in serpents, is a specially modified form of saliva, and 
there are also smaller teeth on the palate. As these 
poisonous lizards are certainly not the ancestors of snakes, 
it is quite evident that their poison-apparatus and specially 
Fig. 8. Side view of Upper Dentition modified teeth have been developed quite independently 
rape eee of those of the venomous serpents.. 
The chief interest connected with the dentition of snakes is concentrated on that 
of the highly venomous species. It should, however, be mentioned at the outset that 
there is no sharp line of demarcation between harmless and poisonous forms, which 
are connected by almost imperceptible gradations. Ordinary harmless snakes have two 
rows of short and sharp teeth in the upper jaw (of which the inner series is attached 
to the bones of the palate), and a single row in the lower jaw. In certain species, 
all of which appear to be more or less noxious, one or more of the inner row of 
upper teeth, either in the front or back of the series, is enlarged and furnished with 
a groove or a central tube. In the more thoroughly venomous species, on the other 
hand (Fig. 8), the front of the upper jaw is armed with a 
pair of long tubular teeth, which, when at rest, lie nearly 
flat on the palate, but when in action are raised, by a 
special mechanical arrangement of the bones and muscles of 
the skull, into a nearly erect position. The secretions of the 
large poison-glands are forced through the open bases of 
the venom-teeth by muscular action when the snake opens 
its mouth to bite, and escape into the wound from the 
extremities of the tubes. The emission is so forcible that 
the venom may often be seen to spurt out from the fangs. 
Such delicate weapons are naturally very liable to injury; | 
” S ‘ . . _ t F 5 4 Fig. 9. Palatal View of Upper 
and in order that the snake may not be deprived of their TaakGon of Una Meco, 
Fig. 7. Dentition of Iguana. 
