1876.] Poison-fangs of Snakes. 261 



On the other hand, in the colubrine poisonous snakes, approximating 

 more nearly to the harmless snakes in having a fixed maxilla, sometimes 

 carrying other teeth in addition to the poison-fang, the successional 

 poison-fangs are developed in a single series, like any other Ophidian 

 teeth. 



The development of the individual tooth -germ presents one feature of 

 very great interest. A poison-fang tooth-germ is first formed, like any 

 other, of an extinguisher-shaped enamel-organ (derived from an ingrowth 

 of epithelium, which winds in and out amongst the tooth-sacs) and of a 

 simple conical dentine-pulp. 



As it elongates, a groove appears on one side, which, by deepening and 

 by the approximation of its lips, becomes ultimately converted into the 

 poison-canal. The enamel-organ, with its characteristic enamel-cells, 

 passes without break or alteration into this groove; but still lower down 

 is the tooth-germ, where the groove has become very deep; instead of the 

 prismatic enamel-cells constituting a regular pavement epithelium, we 

 have a reticulum of stellate cells, just like that gelatinous stellate tissue 

 which forms so large a part of a mammalian enamel-organ. That the 

 stellate reticulum is a non-essential structure I have previously shown ; 

 but the occurrence of such a tissue within the poison-canal, which it 

 wholly occupies, and in which it represents the prismatic enamel-cells 

 found higher up, strongly suggests the idea that it is a sort of retrograde 

 metamorphosis of an active enamel -forming tissue into one which simply 

 fills up a void. 



It need hardly be added that a thin layer of enamel is developed upon 

 the outside of the poison-fang ; but none is formed on the interior of 

 the poison-canal. 



The base of a poison-fang is fluted (this is not the case with other 

 Ophidian teeth), the dentine being convoluted as it is in the base of the 

 tooth of Varanus or in a labyrinthodont tooth ; and it is attached to the 

 bone through the medium of an opaque, ill-defined, calcified material, 

 beyond which again comes a coarse bone. The fixation of a tooth is 

 effected (alike in cobra and in viperine snakes) by a sort of scaffolding 

 of coarse-textured bone, which is very rapidly thrown out from the 

 surface of its finer textural maxillary bone. This " bone of attachment," 

 met with, as I have elsewhere pointed out, in greater or less quantity 

 wherever teeth are attached by ankylosis, is entirely removed with the 

 fall of a tooth, and is developed afresh for its successor. 



