ABSTRACT
Hydrocephalus (in the vernacular, water on the brain) in practice means enlarged cerebral ventricles. The term ‘external hydrocephalus’, which denoted enlargement of the cerebral subarachnoid spaces, has dropped out of use, as it is no more than an aspect of cerebral atrophy. The terms ‘communicating’ and ‘non-communicating’ hydrocephalus are still used. They denote the presence or absence of communication, via the apertures of the fourth ventricle, between the ventricular system and the subarachnoid space. Mention has already been made (p.29) of naked-eye changes in cases of hydrocephalus, and of some of the causes of ventricular enlargement.
