FRESH-WATER SNAKES. 223 



s'ouvre dans la bouche derriere le fourreau de la langue . . . 

 elle s'eleve pour se presenter dilatee sous les arriere- 

 narines.' 1 The glottis of water snakes must have a still more 

 upward direction to present itself to those air passages. 

 Perhaps water snakes do not require to yawn so frequently 

 as is the habit of their terrestrial relatives ; and if they do, 

 it must be a rare privilege to be able to inspect the process, 

 as one can so frequently do with the pythons and vipers at 

 home. Our authorities do not give us much information 

 on this point.^ 



Their moderately long tapering tail is used as a propelling 

 power. Exteriorly, too, water snakes have smooth non-imbri- 

 cated scales, though exceptions exist in those species which 

 frequent both land and water, as the Ti'opidonoti, a large 

 family of which our common English ring snake is a member, 

 and which, as their name denotes, have all keeled scales, from 

 rpomg, Tpo'rridoc, a kcel. These, also, can elevate their ribs, and so 

 flatten the body in the water, another assistant in swimming. 



A marked exception to the sm.ooth-scaled, water-loving 

 snakes is the African viper, known as the ' River Jack ' 

 from its partiality to water. Vipcra rJiinosccros, from the 

 spinous scales which have the appearance of horns on its 

 nose, is allied to those described in the i8th chapter. Though 



1 Dumeril et Bibron, Erpefohs^ie generak, tome i. p. 179. 



' Since this has been in type, there has been brought to the Gardens an Indian 

 ' River snake ' ( Tropidonotiis quincimciatits), affording me an opportunity to 

 observe that there is a notable modification of the glottis, as also of the nostrils. 

 Not a true water snake, but one of the intermediate families, so do we find the 

 nostrils somewhat higher than those of land snakes, while yet not quite on the 

 top of the snout as in sea snakes ; the glottis has a corresponding upward direc- 

 tion to meet them, and is a more elongated, longitudinal slit than those furnished 

 with \.\\Q petite languette. — June 1S82. 



