78 
ON THE PHYSIOGNOMY OP SERPENTS. 
PORMS. 
Ophidians differ infinitely from each other relatively to 
their size and their general form. This depends in a great 
measure on their mode of life, the nature of the places, 
or the element they inhabit, and also on the kind of loco- 
motion which is natural to them. The species which 
frequent trees are especially distinguished by their slender 
forms ; while those which prefer plains, or retire into bur- 
rows, are recognisable by their compact body, terminated 
by a very short tail ; intermediate between these two tribes 
as to development of parts, are a great many serpents that 
prefer to remain on the ground always, but can climb, and 
also swim, with greater or less facility ; others that delight 
more in humid places, or never quit the water, present the 
most varied forms, more or less suited to this species of 
locomotion. 
A Trunk laterally compressed, is observed in the greatest 
number of Ophidians ; but no family presents this charac- 
ter in so marked a degree as those Tree-snakes which we 
have included in the genus Dipsas, and Sea-serpents which 
have the belly more or less completely keeled^ in order 
better to cut the waters. The serpents, on the other hand, 
which merit more especially the name of terrestrial, such 
as the Tortrix, the Calamaria, the Elaps, &c., are dis- 
tinguished by bodies more or less cylindrical. Others, 
such as the Tropidonotus, equally terrestrial, but excellent 
swimmers, have a belly very broad, and rounded towards 
the sides. Several Boas have the faculty of rendering 
their trunk, when gliding or swimming, of the same form 
as the Tropidonotus ; but their trunk becomes laterally 
compressed by an opposite movement of the ribs, when 
they prepare to climb or to roll themselves inwardly. 
These changes in the size of the trunk which take place in 
such movements are found in a greater or less degree in 
all Ophidians, and render the exact determination of their 
forms very difficult : for indicating that of the body we are 
obliged to describe the figures which transverse sections 
present, one of which is made in the middle of the trunk, 
