Introduction

The skull is composed of 22 separate bones, most of them paired. It can be divided into a robust calvarium that surrounds and protects the brain, and a delicate facial skeleton composed mainly of thin walled bones, some of which contain air-filled cavities known collectively as the para-nasal sinuses. The cranial cavity contains the brain and the intracranial portions of the cranial and spinal nerves; the blood vessels that supply and drain the brain and the haemopoietic marrow of the overlying bones; the meninges (dura, arachnoid and pia mater) and the cerebro-spinal fluid.