Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: grooves for the meningeal vessels. It is important to remember in trephining that the inner table is not always parallel with the outer. CHAPTER IIT. THE CRANIAL CONTENTS. The membranes of the brain.—The dura mater, from its toughness, forms an excellent protection to the brain. It is very intimately adherent to the bone over the whole of the base of the skull, and consequently in this situation extravasations between the membrane and the bone are scarcely possible. Over the vault its attachments are comparatively loose, although it is more closely adherent along the lines of the sutures. This lax attachment allows large haemorr- hagic and purulent extravasations to collect between the dura mater and the bone. Such extravasations usually lead to compression of the brain, and it may be noted that in the great majority of all cases of compression the compressing force is outside the dura mater. Thus, in uncomplicated cases, when symptoms of compression come on at the time of an accident, the cause is probably depressed bone; when they appear after a short interval, the cause is probably extrava- sated blood between the membrane and the bone ; and when a long interval (days or weeks) has elapsed after the accident, the cause is probably a collection of pus in the same situation. When blood is poured out between the dura mater and the bone in cases of fracture, the vessel that, as a rule, gives way, is the middle meningeal artery. In thirty-one cases of such haemorrhage, this vessel wasthe source of the bleeding in twenty-seven instances (P. Hewctt). The artery is most often torn, as it crosses the anterior angle of the parietal bone. There are many reasons for this : the bone where grooved by the artery is very thin; the artery is often so imbedded in the bone that fra...