The cranium must be perforated, however, when the existence and site of abscess under the bone is distinctly marked: and in such cases the practitioner is much to blame if he does not give his patient a chance of recovery by the operation: many are lost by its not being performed, and the following case is a striking example of such negligent practice. A young female fell from a great height amongst some rubbish, and sustained a severe blow on the left side of the os frontis, a considerable portion of which was thereby denuded. She seemed to be doing well for some time; but about the eighth day after the accident, pain in the head, with vertigo, rigors, and sickness, febrile excitement, and a white and dry state of the bare portion of the bone, supervened. She was depleted copiously, but notwithstanding all the symptoms indicating formation of matter under the exposed bone were present, the operation of trephine was deemed inadvisable. Severe rigors continued; she became affected with spasmodic twitchings of the muscles of the face, and stiffness of the jaw, neck, back, and breast, and was, in short, allowed to die. On the dissection, the dura mater below the diseased bone was found separated to a very considerable extent, and the cavity was filled with thin purulent matter; the abscess extended along the superior longitudinal sinus, and communicated with this vessel through an ulcerated aperture; the canal was filled with pus, as far as its junction with the transverse sinus, near which point its cavity was obstructed, and the abscess limited by a firm plug of lymph. A small abscess had formed between the bone and pericranium, above the extensive collection within; the internal table of the diseased bone was fractured and slightly depressed, and its fractured edge was rough, sharp, and projecting. But the operation may sometimes fail to prove beneficial; the brain may have become diseased, as well as its membranes, or the patient may not recover from the irritation caused by the abscess, and the depressing tendency of the antiphlogistic treatment which may have been put in force, previously to the formation of matter. But still there is a probable chance, after the collected matter has been evacuated by the operation, of the dura mater granulating, the cavity filling up, the membrane becoming adherent to the cranium around the aperture, and the patient regaining his former health and vigour. If, after removing a portion of bone on account of symptoms of suppuration in that situation, the dura mater be found adherent, and of a healthy appearance, the surgeon is scarcely justified in going deeper in search of effused fluid: the evils liable to result from wounds of the dura mater have been already mentioned, and illustrated by an example. The operation of trephine must also be resorted to in cases of punctured fracture. One perforation will generally be sufficient to enable the surgeon to remove the detached fragments of the inner table.