In patients at the middle period of life, a different feeling and sound is communicated to the operator after having cut through the outer table of the skull. Whether this change is experienced or not after getting to some depth, he ought to proceed cautiously, moving the saw lightly, quickly, and sharply, in the direction of the teeth, and using no pressure. The operator should not be hurried, for he is apt to do harm if he is; there is no inducement to make great haste, for the patient does not suffer much, if any pain. After every two or three turns of the saw, it is prudent to examine the track with the flat end of a probe, or with a toothpick. If the perforation is found to be completed at any point, then the instrument is to be inclined to those which are undivided; and the fluted crown allows of this being done with great facility. After the circle of bone is separated on all sides, it is to be removed by forceps, or by means of the lever; and the sharp points ought to be taken from the edge of the perforation by means of the latter instrument, otherwise the dura mater may be fretted and torn when following the natural motions of the brain. The lever must be strong, and simple in its construction. And after a sufficient space of bone has been removed, its point is to be introduced cautiously under the part that requires elevation; the edge of the sound bone at various points affords a fulcrum, and by persevering and steady efforts, the object of the operation will be accomplished. The dressing of the wound should be simple; the integuments are made to cover the aperture, or as much of it as possible, and due support is given by compress and bandage. The after-treatment must be varied, and conducted according to circumstances. It may become necessary to repress the granulations, or else to soothe the wound and abate inflammatory action in the surrounding parts. Perhaps incisions may be required, to prevent the formation of matter, and destruction of the cellular tissue, and of the tendinous expansion, or to evacuate fluid already secreted. The patient’s strength may require support. He may stand in need of stimulants; or, on the contrary, the most active means may be required to subdue vascular action, and to prevent the evil consequences which would result to the important parts within the cranium from such over-action.