The meningophylax was a small plate, which was inserted under a bone which was being cut in order to protect underlying structures. 'In cutting or sawing the bone,' says Paul (VI. lxxvii), 'when any vital parts are situated below, such as the pleura, spinal marrow, or the like, we must use the instrument called the meningophylax for protecting them (μηνιγγοφύλακα).' Celsus thus describes it (VIII. iii): Factis foraminibus eodem modo media septa, sed multo circumspectius, excidenda sunt, ne forte angulus scalpri eandem membranam violet; donec fiat aditus, per quem membranae custos immittatur; μηνιγγοφύλακα Graeci vocant. Lamina aenea est, firma paulum resima, ab exteriore parte laevis; quae demissa sic ut exterior pars eius cerebro proprior sit, subinde ei subiicitur quod scalpro discutiendum est; ac si excipit eius angulum, ultra transire non patitur; eoque et audacius, et tutius, scalprum malleolo medicus subinde ferit, donec undique excisum os eadem lamina levetur, tollique sine ulla noxa cerebri possit. Pl. XL, fig. 3 shows a figure of the meningophylax from Vidius. _Drill._ Greek, τρύπανον; Latin, _terebra_, _terebella_. There are, says Celsus, two kinds of drills. The first like those used by artisans and driven by a thong, the second with a guard to prevent the instrument from sinking too deeply into the bone. The drill was used in excising a piece of the skull where the diseased portion was larger than could be comprehended by the modiolus of a trephine. The part to be removed was surrounded by perforations with the drill and the intervening spaces were divided with chisels or raspatories. Celsus says: At si latius vitium est quam ut illo comprehendatur, terebra res agenda est. Ea foramen fit in ipso fine vitiosi ossis atque integri; deinde alterum non ita longe, tertiumque, donec totus is locus qui excidendus est his cavis cinctus sit. Atque ibi quoque, quatenus terebra agenda sit, scobis significat. Tum excisorius scalper ab altero foramine ad alterum malleolo adactus id quod inter utrumque medium est excidit; ac sic ambitus similis ei fit qui in angustiorem orbem modiolo imprimitur (VIII. iii). Paul says: 'If a weapon be lodged deep in bone of considerable thickness it may be bored out with drills' (τρυπάνοις) (VI. lxxxviii). Aretaeus (ed. Adams, p. 467) says that exposed bones are to be surrounded with perforations by means of the drill and thus reduced (τερέτρῳ χρὴ περικόπτειν τὰ γυμνά). The boring parts of drills are not unfrequently found. The most ancient illustrations known to me of drills driven by thongs are in the work by Vidus Vidius (_Chirurgia e Graeco in Lat. Conversa_, V. Vidio. Florent. interprete c. nonn. eiusd. commentariis. Lutec. Paris., 1544).