44 OPHIDIAN EEPTILES. 



" Although these five groups/' remarks Dr. Giinther, " are not 

 separated from each other by defined lines of demarcation, and 

 frequently pass into one another by intermediate forms, yet a 

 family and genus which should be composed of species of several 

 of these groups would be a very unnatural assemblage of hetero- 

 geneous forms." 



It is also remarked by the same naturalist that there is no sharp 

 boundary line between the order of Snakes and that of Lizards. 

 There are various limbless Saurians of Ophidian appearance, but 

 the systematic position of which is decided by the structure 

 of their jaws. The Common Orvet, or Slow -worm, is a familiar 

 instance. On the other hand, certain Ophidians remind us, by 

 several characters, of the Saurian type, as the Snakes constituting 

 the families Typhlopida, Tortricidce, Xenopeltida, and Uropeltida, 

 which are distinguished by polished, closely adherent, rounded, 

 sub-equal scales, much resembling the smooth scales of various 

 Scincoid Lizards ; most of them have a very narrow mouth, un- 

 like the enormous gape of the typical Serpents, and some are 

 without that longitudinal fold in the median line of the chin 

 which is so characteristic of most Ophidians ; moreover, most 

 of them have rudiments of the bones of a pelvic arch. " The 

 reason," alleges Dr. Giinther, " why we adopt the view of those 

 systematists who refer such reptiles to the Ophidians, instead of 

 associating them with the limbless Scincoid Lizards, is the loose 

 connection of the jaw-bones, a character which must be con- 

 sidered as peculiar to the Ophidians, and which is only somewhat 

 less developed in the families mentioned than in the typical forms. 

 The two halves of the lower jaw in Ophidians, namely, are not 

 united by a bony symphysis, but by an elastic ligament. The 

 peculiar mobility of the jaw bones enables the Snakes to extend 

 the gape in an extraordinary degree, and to work their prey down 

 through the collapsed pharynx." 



The same naturalist classifies the Ophidia into three sub- orders, 

 in which the venemous Snakes are separated from the others ; but 

 to some herpetologists this arrangement must appear rather forced, 

 as his Venemous Colubrine Snakes have certainly a much nearer re- 

 semblance in other respects to the Colubrida than they have to the 

 Viperine Snakes. For the most part, these reptiles are provided 



