Another erroneous impression regarding fangs has been produced by confusing those that are ‘fixed’ and those that are ‘moveable.’ All truly are fixed firmly into the jaw; but in the viperine snakes the very short bone itself is moveable by a volitionary action, so that it partially ‘rotates,’ and with it the fang. The _Elapidæ_ have fixed or ‘permanently erect’ fangs, and when the mouth is closed these fit into a depression in the lower jaw. Viperine fangs only can be erected or depressed at pleasure. It is those which spring into place for use like a pen-knife half opened, and which when at rest are folded back, like the knife shut up again. This action has been most lucidly described by Coues in connection with the _Crotalidæ_, under which head I will quote from his paper. Schlegel himself is not very clear in his distinctions between those serpents that have ‘moveable’ fangs and those which have not, but Cuvier had already described them as _crochets mobiles_. Indeed, it is since the date of Schlegel’s work that more complete investigations have revealed closer anatomical distinctions. We therefore find in some of our highest-class encyclopedias, if not of recent date, mis-statements regarding fangs which unfortunately have been quoted in many works. ‘Venomous serpents depress their fangs,’ says Schlegel’s translator, true to the text, but as if it were common to all. Describing deglutition, Schlegel says ‘the same in all’ ‘_sans en excepter les venimeux, qui lors de cet acte redressent leur crochets et les cachent dans la gaine des gencives, pour ne point les exposer à des injures_.’[96] This, however, is the case with the _Viperina_ only. It is common, for the reasons just now assigned, to find the cobra classed among the vipers, in some popular encyclopedias; and in one, a valuable and generally trustworthy American edition of 1875, we read, ‘moveable fangs like the cobra, viper, and rattlesnake.’ A cobra has _not_ moveable fangs. Another, an excellent English edition, but of not very recent date, includes _all_ venomous snakes under the head of ‘vipers;’ a third in general terms states that ‘venomous snakes have no teeth in the upper jaws, excepting the fangs, and that the opening of the mouth brings these into position;’ whereas it is now known that a viper can open its mouth and yet keep its fangs depressed and sheathed. In several other encyclopedias the description of fangs is suited to vipers only. It is not necessary to designate names, as these things will be set right in the new editions. They are mentioned more with a view to show that ophiology has advanced with rapid strides of late, rather than presumptuously to criticise our standard works. Perhaps in another twenty years my own poor efforts will be exposed as ‘old-time misconceptions.’