Neither of these experimentalists stated positively that the reserve fangs were in connection with the duct, a phenomenon which I believe is still unexplained. Fayrer removed the functional fangs from an _Echis carinata_, and observed that there were no others fixed at the time, though there were others loose in the mucous membrane. _On the fifth day another pair were anchylosed and ready for use!_ As will be presently seen, this little viper of sixteen or eighteen inches (almost too small to recognise near the great python in the frontispiece), displays corresponding vigour both in the potency of its venom and in the renewal of its weapons. From the foregoing illustrations of numerous pointed teeth, the question might arise, ‘How are they disposed of when the mouth is closed? and from the narrow space which is apparent in the flat head of a snake, and the close fit of the jaws, how do the four or six rows meet without interfering with each other?’ This difficulty is obviated by the teeth _not_ closing one upon the other as ours do. Nor are the palate teeth in the centre, or they would wound the upper part of the trachea and the tongue sheath, which occupy considerable space. They close down on each side of these organs. ‘Every relief on one surface fits into a corresponding depression on the other surface, and accurate apposition of every part is obtained,’ Nicholson explains to us. ‘The four upper rows of teeth divide the roof into three parts, and the lower jaw teeth fit between the upper maxillary and palatine teeth.’ There remains yet much more to describe in connection with the poison fang, which might come in the present chapter; but as the two following will treat of the _Viperidæ_ and the _Crotalidæ_—the dentition being the same in both—the viperine fangs shall claim further space under those heads. These three consecutive chapters, and also chap. xxii. on some exceptional forms of dentition, must necessarily be somewhat blended; but I divide them thus in order to present the distinct families more clearly, and render the subject less tedious to the reader. [Illustration] [Illustration] CHAPTER XX. _VIPERINE FANGS._ THOUGH the ensuing chapter will be devoted more exclusively to the _Crotalidæ_ or rattlesnakes, it were well to repeat here that the two families _Viperidæ_ and _Crotalidæ_ comprise the sub-order of Ophidia ‘VIPERINA,’—those that have the isolated, moveable fangs, the term _isolated_ having reference to the functional fang only. It may appear incongruous to present the illustration of a viperine jaw with a whole cluster of fangs, while affirming that there is the one pair only; but the pair in use are ‘solitary,’ because the jaw bears no simple teeth, as in those with fixed or permanently erect fangs.