144 REPTILES 



to the noxious representatives of these reptiles. Ordinary 

 harmless snakes have, as a rule, two rows of teeth in the upper 

 jaw-bone, or maxilla. In the pythons and boas (Boidce) as 

 well as in the typical section of the family Colubridce, as repre- 

 sented by the English grass-snake {Tropidonotus natrix), all the 

 teeth are solid, and these snakes are non-venomous, although 

 the larger kinds are capable of inflicting a severe bite. The 

 section of Colubridce with this type of dentition is known as the 

 Aglypha or solid-toothed colubrines. There is, however, an- 

 other section termed the Opisthoglossa, or back-fanged colu- 

 brines, in which some of the hind maxillary teeth are grooved 

 and connected with a small poison-gland. The group is not a 

 very numerous one, and is best known in the shape of some of 

 the Indian tree-snakes of the genus Dipsadomorphus. The 

 poisonous properties of these snakes are not great, but they 

 are sufficient to paralyse the small animals on which these 

 reptiles subsist. Far more venomous are the members of a third 

 group of Colubridcs, the Proteroglypha, or front-fanged colu- 

 brines, among which are included the deadly krait and cobra as 

 well as the sea-snakes. As their name implies, these snakes are 

 characterised by the circumstance that some of the anterior 

 maxillary teeth are enlarged and grooved or channelled for the 

 conveyance of venom from the poison-glands. The remarkable 

 feature connected with the presence of venom-teeth in the 

 Opisthoglypha and the Proteroglypha is that their development 

 has apparently taken place independently in the two groups. 



A third independent development of venom-teeth seems to 

 have taken place in what may be called the typical venomous 

 snakes, namely vipers and rattlesnakes, constituting with their 

 allies, the family Viperidce, although they are really not more 

 poisonous than cobras and kraits. In these snakes the apparatus 

 is of a different nature to that of the venomous ColubridcE, for 

 the maxillae, except for the undeveloped successional ones, only 

 carry a single pair of teeth, which are of such length as to be 

 denominated fangs, and are capable of erection and depres- 

 sion ; assuming the erect position automatically as soon as 

 the mouth is opened. These fangs are grooved or channelled 

 for the conveyance of the venom ; the grooves or channels are 

 in connection with the ducts of the poison-glands, which are 

 situated on each side of the head, and correspond to the salivary 



