80 ON THE PHYSIOGNOMY OF SERPENTS. 



animal suspended from ta single point. The s^\^mming 

 Boas have not a different formation of the tail ; and it is 

 only in the Acrochordus that it becomes slightly com- 

 pressed. The end of the tail is most frequently fortified 

 by a simple conical scale, more or less pointed or hooked ; 

 this point is converted in the Crotalus mutus into a hard 

 spine ; but the other Crotali have the tail furnished ^\^th 

 a peculiar rattle, often very large, althougli it is but a 

 simple production of the epidermis. 



The Head does not always present any correspondence 

 in form with the other parts of the body. It is, for ex- 

 ample, very compact and thick in the Dipsas, which, how- 

 ever, has a very elongated body, as occurs also in the Den- 

 drophis, althougli the head of the latter is very long and 

 slender. Hence it may be perceived that the form of the head 

 is chiefly influenced by the kind of food which nourishes 

 the species. Those which swallow animals large in pro- 

 portion to their own size have necessarily a large head, the 

 parts of which can dilate, forming a contrast to what is 

 found in those which live on worms, insects, or animals of 

 small size or of slender forms. In such, the head is scarcely 

 distinguishable from the trunk ; it is generally short, 

 roimded, and thick at the muzzle, as in the Tortrix, the 

 Calamaria, the Elaps, &c. In the first kind of snake, on 

 the contrary, the head is very broad at the base, very dis- 

 tinguishable from the trunk, and consequently very suscep- 

 tible of an extraordinary degree of dilatation, as is especially 

 the case with the venomous serpents, properly so called, 

 and wnth several species of Dipsas, Xenodon, Boa, Coluber, 

 &c. The Muzzle determines the general form of the head ; 

 it is sometimes short and thick, sometimes rounded or 

 truncated, at other times slender and pointed ; in some it 

 terminates in a hard turned-up scale ; in others it is drawn 

 out into a fleshy and moveable appendage. Sometimes, as 

 in the Homalopsis Herpeton, we observe these appendages 

 on each side of the snout ; but those which some Vipers 

 have over the superciliary region are merely scales with 

 pointed prolongations, more or less developed. The point 

 of the muzzle always overlaps the lower jaw, the edges of 

 which are lodged within those of the upper jaw ; but the 



