FOEMS. 
81 
grooved passage of the rostral plate allows the tongue to 
be projected, and prevents the mouth from being entirely 
closed ; and it is only in aquatic serpents that the ends of 
the jaws are so exactly shut up as to render the entrance 
of water impossible. 
The ^position of the Eyes and of the Nostrils depend on the 
mode of life of the species. Aquatic snakes often have 
these organs but little developed ; they are directed to the 
sky, and consequently placed on the top of the head ; and 
it is the same with the Tortrix and some terrestrial serpents ; 
in others, especially in tree-snakes, they are large and more 
or less lateral. Terrestrial venomous serpents often have 
very wide nostrils ; and there is a whole family of the true 
venomous serpents in which these organs are accompanied 
by a second aperture in the maxillary region, which seems 
to have the function of an accessory organ of smell. It 
ought to be remarked, that the fossettes sunk in the lips 
of several Boas have no communication with the interior of 
the head, and therefore they present no analogy to those of 
the Trigonocephalus and Crotalus. 
The Mouth of Ophidians, more or less deeply cut ac- 
cording to the degree of dilatation of which the parts of 
the head are susceptible and the form of that organ, some- 
times presents straight margins ; sometimes they are in the 
form of an s ; and sometimes they mount at an angle more 
or less obtuse towards the commissure of the lips. The 
diversities of form and disposition of the parts of the head 
of Ophidians which we have mentioned, give to each species 
a peculiar physiognomy, the more characteristic as their 
features are more prominent ; when imprinted on the 
memory, it serves for the recognition of the numerous races 
of these interesting animals. The circumstances which 
chiefly contribute to render the physiognomy of serpents 
characteristic, are a large broad head, high, angular, cordi- 
form, and covered with small scales with unequal surfaces, 
a wide mouth curved at its margins, thick lips, large fos- 
settes on the sides of a muzzle truncated or turned up at 
the end, small eyes, with an elongated pupil, and overhung 
by salient superciliary plates — characters which are gene- 
rally united in the species with clumsy forms, such as we 
