142 CLASSIFICATION OF AMPHIBIANS. 



almost entirely upon that knowledge -vvMch is gained by 

 analysis ; and in regard to the present group^ it is im- 

 possible to determine whether a part of the dipod ophi- 

 dians do not really enter into this circle^ or whether 

 they belong to the Saures. We therefore proceed to 

 the two typical families. 



(1-il.) The CoLL'BERiD^^ or true snakes^ are consi- 

 dered by ]\I. Cuvier as following the slow-worms — a dis- 

 position which in every respect is natural^ because it is 

 demonstrable by analogy. The point of junction^ however, 

 has not clearly been ascertained. M. Cuvier, speaking 

 of the genus Typhlops, observes that they are small 

 snakeSj which^ on a careless glance, resemble slow- worms. 

 On entering upon this family, however, we find most of 

 the characteristic properties of the ophidian reptiles 

 highly developed : one of these is the power of dilating 

 the throat to such an astonishing degree, as to admit the 

 swallowing of animals much thicker than the serpent 

 itself. The following anatomical facts will explain this. 

 The tympanic bone, or pedicle of the lower-jaw, is mo- 

 bile, and almost always suspended to another bone, 

 analogous to the mastoidian, attached on the cranium 

 by muscles and ligaments which permit its moving : 

 the branches, likewise, of this jaw are united to each 

 other, and those of the upper jaw to the intermaxillary 

 only by ligaments, so that they can, in a greater or less 

 degree, be separated. The palatine arches are also move- 

 able, and are armed with sharp teeth curved backwards ; 

 but these teeth are fixed, and are not perforated like 

 those of the next family : the branches of the upper 

 and under jaws are furnished for their entire length with 

 these teeth : there are consequently four ranges in the 

 upper part of the mouth, and two in the under. Such 

 appear to be the leading anatomical peculiarities of this 

 family, the most numerous in species, and in the vari- 

 ations of their forms, of any in the whole tribe. The 

 sub-divisions, consequently, are very many ; but as these 

 have been made with the sole object of distinguishing 

 structure, without any reference to the affinities and 



