56 INTRODUCTION 



median line in such a way that the inner wall of 

 the tooth is in reality the anterior surface, and 

 the outer wall the posterior surface, of the ordinary 

 tooth. 



Grooved teeth, with open canal, are situated either 

 at the anterior extremity (Proteroglyphs) or at the 

 posterior extremity (Opisthoglyphs) of the maxillary 

 bone, usually followed or preceded by a series of solid 

 teeth, which in some cases may likewise show a 

 more or less distinct groove. Such may also be 

 present on the teeth of the lower jaw, as in the Euro- 

 pean Ccelopeltis, in some specimens of which a faint 

 groove is visible on the outer side with the aid of a 

 strong lens. 



The tubular fangs of the Viperidae are inserted on 

 the posterior extremity of the much abbreviated and 

 erectile maxillary bone, which bears no other teeth. 

 The Proteroglyphs (Cobras, Coral-snakes, Sea-snakes) 

 and the Solenoglyphs (Vipers, Pit-vipers, Rattlesnakes) 

 may be regarded as the diverging extremes in the 

 development of the poison apparatus, both culmina- 

 ting in forms with tubular fangs, the former as de- 

 rived directly from the Aglyphs (harmless snakes), 

 the latter from the Opisthoglyphs, likewise evolved out 

 of the Aglyphs. That the insertion of the poison 

 fangs of the Viperidae is really on the posterior 

 extremity of the maxillary bone is evident from the 

 condition of the bone in its recumbent position, 

 especially in the African Viper, Causus, which in 



