There are two ways of cutting out a bone; if the part injured be very small, by a modiolus, which the Greeks call chœnicion[ HZ ], if larger by terebræ. I shall explain the method of each. The modiolus is a concave and round iron instrument with serrated edges in its lowest extremity; through the middle of which is put a pin, surrounded also by an interior circle. Of perforators there are two kinds: one of them resembling that, which carpenters use; the other with a longer head, which begins from a sharp point, and then turns quickly broader; and again from another beginning goes upward with thickness pretty near equal.

If the disease be confined to a small space, so that the modiolus can cover it, that must be used preferably. But if a caries appear below, the pin in the middle is put into the opening. If there be a blackness, a small hole is made by the angle of a chisel(13) to receive the pin, that the modiolus resting upon that, by being turned round may not slip, and then it is turned like the perforator by a strap. And there is a certain degree of pressure required, that both a perforation may be made, and it may go round; because if it be lightly impressed, it does not produce the effect; if too much, it has no motion. And it is not improper to drop in a little rose oil or milk, the smoothness of which may make it turn with the greater ease; yet too much of the liquid blunts the edge of the instrument. But when the modiolus has marked out a way for itself, the middle pin is taken out, and it is worked about by itself. And then, when the soundness of the inferior part is discovered by the dust, the modiolus is taken away.

But if the disease is more extended than to be covered by that, we must make use of the perforator. By this a hole is made in the limit, that divides the injured from the sound part of the bone; and not far from that a second, and a third, till the part, that is to be cut out, be surrounded with these holes. And in this case too the dust indicates how deep the perforator is to go. Then a chisel being drove by a mallet from one hole to another, cuts out the intermediate space between them; and thus a circumference is formed like to that, which is imprinted in a smaller circle by the modiolus. In whichever way the circle has been made, let the same chisel, laid flat on the corrupted bone, smooth each superior lamina, till the bone be left entirely sound.

A blackness hardly ever goes quite through a bone, but a caries does, especially where the skull is faulty. There also the disorder is discovered by the probe, which being introduced into the hole, that terminates at the sound part of the bone, both finds some resistance, and comes out moist. If it prove pervious, the probe going in deeper between the bone and the membrane, meets with no resistance, and comes out dry: not because there is no corrupt sanies within, but because it is there diffused, as being in a larger cavity.

Now whether a blackness, which the perforator has discovered, or a caries, which the probe has shewn, pass through the bone, the use of the modiolus is generally fruitless: because, where the disease has penetrated so deep, it must also necessarily be largely extended in breadth. Here then we must use the second kind of perforator above described; and to prevent its growing too hot, it must be dipped now and then in cold water. But then we must proceed with greater caution, when we have perforated either half through in a simple bone, or the superior lamina in a double one. The space itself guides us in the first case; and in the other, the blood. Therefore at that time the strap must be drawn slower, the left hand should press more gently, and be taken off pretty frequently: also the depth of the perforation is to be considered, that we may be sensible whenever the bone is broke through, and run no risque of wounding the membrane of the brain by its point, from which proceed violent inflammations, with danger of death.

When the holes are made, the intermediate spaces must be cut out in the same manner, but with much more circumspection; lest the angle of the chisel chance to wound the same membrane; till a passage be made, through which the instrument to protect the membrane may be introduced. The Greeks call it meningo-phylax[ IA ]. It is a copper plate, firm, bent a little upward towards the end, and externally smooth: which being introduced in such a manner, that its external surface be next the brain, is put under that part, which is to be separated by the chisel; and if it receives its angles, it stops its progress; and upon this account the physician repeats his strokes upon the chisel both more boldly, and more safely, till the bone being cut out all round is raised by this plate, and may be taken away without any hurt to the brain. When the whole bone is taken out, the edges must be scraped round and smoothed, and if any dust has fallen upon the membrane, it must be gathered up. When the superior part is taken away, and the inferior left, not only the edges, but the whole bone must be smoothed, that the skin may afterwards generate upon it without being hurt, which growing upon a rough bone, does not immediately become sound, but produces new pains.

The steps to be taken after the brain is uncovered, I shall mention, when I come to fractured bones. If any base is preserved, medicines not greasy, that are calculated for recent wounds, must be applied, and over them must be laid sordid wool moistened with oil and vinegar. In process of time flesh grows from the bone itself, which fills up the cavity made by the operation. And when any bone is cauterized, it separates from the sound part, and granulations sprout up between the sound and mortified part, which expel what has separated. And this, because it is a thin and small lamina, by the Greeks is called lepis[ IB ], that is, a scale.

It may happen too, that from a blow, a bone may be neither fissured, nor broke through, but the surface of it only contused, and rendered rough. When this occurs, it is sufficient to scrape and smooth it. Though these methods are most commonly practised in the head, yet they are common to the other bones too; so that wherever the like case shall occur, the same remedy must be used. But as they are fractured, fissured, perforated, and contused, they require some particular methods of cure in each kind, and in most of them, some general ones also. Of these I shall proceed to treat, beginning with the head.