This practical investigation no doubt greatly offended the imprisoned patient, for suddenly down came a pair of regular fangs—they _looked_ like fangs;—and as my finger pressed the jaw on one or on the other side, I saw these fang-like teeth move, vibrate, exactly like the viperine fangs. When my finger was removed, up they went, folded back in their sheath in true viperine fashion. My finger got a slight prick, for they were exceedingly sharp; but knowing there was no venom in them, that did not concern me, and in a few minutes the sensation was gone. But how was it that Dr. Stradling had made no mention of this extraordinary viperine mobility of the fangs? And what kind of jaw must a snake have to move its back teeth in this manner! For we saw in the previous chapters that the mobility of the fangs is in proportion to the diminishing length of the maxillary bone, that the excessive mobility of the viperine fang is owing to the greatly reduced size of that bone, that a slight mobility is observable where the jaw is somewhat less reduced, and so on; but here is a harmless Coluber with a jaw long enough to hold five or six fixed, simple teeth, and then an extremely mobile long one at the back. Can the jaw be divided in the middle? Thus I marvelled. ‘Now let us look at Heterodon.’ But that pretty little snake positively refused to open its mouth; so, fearing to alarm it, or cause it to disgorge its last meal, I did not encourage its forcible detention. Not to lose a moment, I then and there pencilled a note to Dr. Stradling, begging him to tell me if he had observed anything unusual in _Xenodon’s_ ‘fangs.’ That I had examined them and seen what appeared very extraordinary; but before describing it, was desirous of having my observations confirmed by him. But the Dr. had been unexpectedly appointed to another ship, which would sail immediately. Many weeks must, therefore, elapse before his reply could reach me.