24 ON THE PHYSIOGNOMY OF SERPENTS. 



themselves to the extraordinary enlargement of the internal 

 parts. 



It results from what we have stated on the nature of 

 serpents, that we might exclude from this order the Am- 

 phibaena and the Typhlops, althougli these last are con- 

 nected in many respects with the Ophidians, and form 

 the transition to these reptiles. It is this approximation 

 which renders it difficult, if not impossible, to establish 

 distinctive characters for the two neighbouring orders of 

 Saurians and Ophidians. Let us illustrate this by some 

 examples. The gular fissure, proper to all Ophidians, 

 except the Acrochordus, is equally seen in several Saurians, 

 such as lizards, &c. Some species of Ophidians shew 

 vestiges of posterior extremities, analogous to those we 

 find in the Apodal saurians, although their structure 

 leads to the belief, that, thougli the animals last mentioned 

 represent the pclWs, Avhile those of the Ophidians corre- 

 spond to the posterior extremities. The structure of the 

 tongue in the Varanus {Monitor, Cuv.) and Teius {Saure- 

 garde, Cuv.), is scarcely distinguishable from those of 

 Ophidians. The want of eyelids does not afford any 

 distinctive character ; for these organs occur in every de- 

 gree of development in the different species of Saurians, 

 Some species, as the Ablepharus and Gymnophthalmus, 

 are totally without them ; the minute eyes of the Amphis- 

 bsena, the Typhlops, and the Acontias ccecus, are covered 

 by the general integument, in such a manner that these 

 animals have so low a degree of vision as to be almost 

 blind ; the Acontias Meleagi'is, on the other hand, has its 

 eyes provided with a lower lid ; the Pygopus presents a 

 rudiment of a cu'cular eyelid round the whole circumfer 

 ence of the eye, without the power of closing that organ ; 

 in several of the Geckos, the eyelids appear as prolonga- 

 tions of the skin, too little developed to serve as a protec- 

 tion to the eyes. One of the most characteristic parts of 

 the cranium of Saurians, is the columella, a small pair of 

 linear bones which unite the parietals to the pteregoids. 

 This bone is wanting, however, in the Typhlops, the Am- 

 phisbaena, and even in the Acontias. The development of 

 the external ear is found in every shade from the Saurians 



