Dein id serrula praecidendum est, quam proxime sanae carni etiam inhaerenti: ac tum frons ossis, quam serrula exasperavit, laevanda est. And Paul says that in amputating a gangrenous limb the flesh ought to be retracted with a band lest it be torn by the saw. Saws were also used in cranial surgery. Hippocrates frequently mentions a saw (πρίων) in this connexion, but it is evident that he means the trephine, as he describes its circular motion. Paul, however, makes it quite clear that he means flat cranial saws, for he mentions both saws and trephines in one paragraph: Ἤδη καὶ τῶν πριόνων τε καὶ χοινικίδων χειρουργίαι, κτλ. 'The method of operating with saws and trephines is condemned by the moderns as a bad one' (VI. xc). Pl. XLI, fig. 3 shows a surgical saw from the British Museum (No. 2,328). It is of bronze, and measures 112 mm. long, 3 cm. broad at one end, narrowing to 23 mm. at the other. There are surgical saws of steel in the Naples Museum. Many of the saws extant are for use as 'frame' saws. Others have the saw portion continuous with the handle, like a knife. Galen (xviii. 331) mentions these 'knife-shaped' saws: 'For in this way each does not become so exactly smooth as with sword-shaped saws (μαχαιρωτῶν πριόνων).' There is an example of this form of saw in the Guildhall Museum, London. _Trephine._ Greek, τρύπανον, πρίων, πρίων χαρακτός, χοινικίς, ὀρθοπρίων; Latin, _modiolus_. The ancient trephine is referred to by Hippocrates, who mentions a saw (πρίων and πρίων χαρακτός) having a circular motion (iii. 374): 'In trephining you must frequently remove the trephine, on account of the heat in the bone, and plunge it in cold water. For the trephine (πρίων), being heated by the circular motion (περιόδου) and heating and drying the bone, burns it and makes a larger piece of bone exfoliate than would otherwise be necessary.' And again: 'You must saw the bone down to the meninges with a serrated trephine (πρίονι χρὴ χαρακτῷ ἐμπρίειν), and in doing so must take out the trephine (πρίονα), and examine with a probe and by other means along the track of the trephine' (πέριξ κατὰ τὴν ὁδὸν τοῦ πρίονος). In injuries to the head in young people (iii. 371) he mentions a small trephine (σμικρὸν τρύπανον), so that apparently several sizes were available. Hippocrates, we have seen, uses the words πρίων and πρίων χαρακτός to denote the trephine. Galen always uses χοινικίς, but in his Lexicon he gives two other words, viz. ὀρθοπρίονι and περητηρίῳ, ostensibly from the works of Hippocrates: Ὀρθοπρίονι--τῇ χοινικίδι. περητηρίῳ--τρυπάνῳ τῷ εὐθεῖ καὶ ὀξεῖ, ἔστι γὰρ καὶ ἕτερον ἡ χοινικίς.