FORMS. 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 



