VENOMOUS SERPENTS. 187 



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 fossse. 



TRIGONOCEPHALUS. 



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 



