be now removed; for which purpose the cranium is to be sawed in a circular direction, about a finger's breadth above the superciliary ridges, and lateral sinuses; the operation must be conducted with great care, or we shall be in danger of wounding the dura mater; the bone must be then divided by a few slight strokes with the chissel and mallet. We shall always find a strong adhesion between the inside of the cranium, and the dura mater; partly, in consequence of the small blood-vessels with which these surfaces are connected, and partly, from the close application of the fibrous structure of the membrane to the bone, and which will vary with the age of the subject, and the form of the skull; the handle of the scalpel carefully introduced will afford the best instrument for overcoming this resistance, and will not be liable to lacerate the dura mater, or to injure the brain. In effecting the separation, the meningeal vessels frequently deluge the whole surface with blood, a circumstance that deserves attention, in as much as their plenitude marks the congestive state of the brain; it shews also that the blood is in a liquid condition, a fact to which some importance has been attached, as it is supposed to occur more particularly in cases of suffocation. The inner surface of the skull may be inspected with the view of ascertaining whether it be carious. The dura mater, thus brought into view, may exhibit marks of inflammation; or coagulated blood or pus may be discovered on its surface, especially in cases where external violence has been inflicted; and it is particularly worthy of notice that such an extravasation, or injury, is not necessarily under the fracture, or part of the cranium upon which the violence that produced it, had been received; on the contrary it often happens that disor-
