Fig. A. Ptyas mucosus, with simple teeth only. That they are not very regular is probably owing to the stages of growth in those that have replaced others.
Fig. B. A venomous snake, Bungarus, the ‘Krait,’ with a fixed fang in front and a few simple teeth behind it.
Fig. C. Jaw of the cobra, with a longer fixed fang, and one or two simple teeth behind it.
Fig. D. The shortest jaw of them all, that of the Indian viper Daboia, in which the maxillary is reduced to a mere wedge of bone. These, with four or five reserve fangs, are here folded back ‘depressed.’ A few palate teeth are also seen.
Having given a slight sketch of the various forms of dentition, and arrived at ‘fangs,’ we may recapitulate, in what Nicholson calls ‘roughly speaking,’ four stages of development in these latter.
First, the ‘fangs’ of the harmless snakes, such as Lycodon, Xenodon, Heterodon, etc., which have no poison gland, but whose saliva may be slightly and occasionally injurious.
Secondly, those having a salivary gland secreting poison and a grooved fang in front of some simple teeth, Hydrophidæ.
Thirdly, the maxillary bone shorter, bearing one poison fang with a perfect canal, and one or two teeth behind it. In some of these there is a slight mobility.
Fourthly, the maxillary bone so reduced as to be higher than long, and bearing only a single tooth, viz. a long, curved, and very mobile fang, Viperina.