SNAKES. 107 



distinguished from the lizards. Those, however, 

 who rely on this character do so on the assump- 

 tion that all limbless reptiles are snakes, and 

 consequently unhesitatingly refer such forms as 

 the common English Slow- worm (Anguis fragilis), 

 the Glass-snakes (Pseudopus gracilis), and other 

 limbless lizards to the members of the Snake 

 family. Since, then, the typical lizard and the 

 typical snake can be so readily distinguished, 

 what are the characters by which the excep- 

 tional limbless types of the one may be distin- 

 guished from the invariably limbless forms of 

 the other group ? 



The limbless lizard will be found to have a 

 distinct external ear in the shape of a more or 

 less well-marked pit lying behind the eye, whilst 

 the two halves of the lower jaw are firmly united 

 in front, and the bones of the upper jaw are 

 firmly fixed to the skull. Further, the tongue 

 in these degenerate forms is never withdrawn 

 into a sheath, and the scales of the belly are 

 not markedly different from those of the back. 



In the Snake, an external ear is never present, 

 the halves of the lower jaw are connected in 

 front only by an elastic band, whilst those of the 

 upper jaw are freely movable on the skull. The 

 tongue is always withdrawn, when not in use, into 

 a sheath, and the scales of the belly are generally 

 very markedly different from those of the back, 

 inasmuch as, with certain rare exceptions, they 

 form a series of broad transverse bands lying one 

 behind the other. These differences are largely 

 connected with the peculiar habits of the snakes, 

 and this significance will be dealt with presently. 



