OF THE MOVEMEIS'TS. 
41 
describe, under the name of Amphisbaana, a serpent fur- 
nished with a head at each extremity, and having the fa- 
culty of moving in opposite directions. A designation ap- 
plied to an Ophidian of the Old World, probably the Eryx, 
is given by modern naturalists, after the example of the 
Portuguese, to some serpents of America. 
The greatest number of non- venomous snakes, and the 
colubriform venomous serpents, defend themselves against 
the attacks of their enemies, by darting at them with an 
elevated head, in order to bite with more effect ; some, 
as the ISTajas, straighten the front of their bodies, and 
take a very peculiar position. Most of them hiss strong- 
ly, as a prelude to the attack ; sometimes also is heard a 
noise from the air, which they forcibly eject from their 
nostrils. Several species throw themselves on their prey 
with huge bounds, seize it generally with the mouth ; 
others secure it by twisting the tail around it ; and the 
Boas also embrace it with the convolutions of their 
trunk. 
The venomous snakes, properly so called, employ the 
same means to procure the animals on which they sub- 
sist, and to rid themselves of their enemies. Indolently 
extended on the ground, they attack indiscriminately 
every animal which disturbs them by too near an ap- 
proach ; but knowing the power of their weapons, they 
are contented to inflict the mortal blow, which but rarely 
misses its aim. To execute this blow, they generally 
straighten the head, carry back the anterior part of the 
trunk, and at a single effort uncoil the folds of their body, 
and support themselves on the tail ; the leap which this 
movement produces may be compared to the recoil of a 
spring, and it directs the wound inflicted by the fangs, by 
a sudden, extremely rapid, downward movement of the 
head. 
OF THE TEETH. 
Ophidians swallow the animals on which they live whole, 
their teeth not serving to chew, nor to break their aliment : 
they are simple dental organs, destined to inflict wounds, 
D 
