The Cerebral Subarachnoid System

In the diagnosis and treatment of intracranial infections and neoplastic diseases, one desires more detailed anatomic knowledge of the cerebrospinal fluid system. Indeed, since the great contribution of Key and Retzius in 1875, little has been added to this knowledge, and the present work has been undertaken in a desire to correct this dearth of detailed information. HISTORY Galen,1father of anatomy, and Vesalius,2in the sixteenth century, described a thin membrane surrounding the brain underneath the dura, but neither of them recognized the arachnoid membrane or the subarachnoid space. In fact, the arachnoid was not established as a membrane separate from the pia mater until the middle of the seventeenth century. It was given its name by Blaes (Blasius),3an anatomist of Amsterdam (1626-1682), arachnoid being derived from the Greek word∥páϰm, meaning a spider's web. Soon afterward, Varioli, an Italian investigator, showed that this membrane