VENOMOUS SERPENTS. 
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their noxious character is expressed in all their parts ; for 
they have a clumsy and ungainly form ; a very short tail ; 
a large head, very wide at the base and heart-shaped, 
all their body is generally rough with lanceolate scales 
surrounded by a very strong carina ; their muzzle is 
often truncated, or even turned-up : their frenal region, in 
several genera, is hollowed out by a wide and deep fossa ; 
the upper lip is inflated, and descends as in the bull-dog ; 
the opening of the mouth is much arched ; the eyes are 
small with a vertical pupil, and buried under a projecting 
superciliary plate ; their fangs are extremely large, and 
alone occupy the maxillary bone, which is reduced to a 
small size, while the external pterygoids form a lever in 
the shape of a stylet. This structure determines the 
nature of their attacks, which are quite peculiar, inas- 
much as they remain quite inactive, until the animals on 
which they feed come within their reach ; when they throw 
themselves on them, strike them at a single blow with the 
fatal wound, which, placing their prey beyond the chance 
of escape, makes it fall into their power. The Venomous 
Serpents, properly so called, are found in the five great 
divisions of the world. Sometimes they inhabit woods, 
sometimes plains. We are acquainted with three genera. 
The two first have nasal fossas. 
TRIOONOCEPHALUS. 
This genus has a tail terminated by a horny and conical 
tip. They inhabit wooded regions in both worlds ; but 
they have not been found in Europe nor in Africa, where 
they are replaced by the Vipers, We can distinguish two 
divisions in this genus, founded on the nature of the tegu- 
ments of the head. 
A. Species with the head covered by scales , — They are 
especially peculiar to the torrid zone. 
1. Trigonocephalus Jararaca. — Form a little more 
slender than usual; head longer, covered with scales, a 
little larger towards the point of the muzzle, of which the 
