A small hollow within the brain that is filled with cerebrospinal fluid

Ventricles:One of the hollow spaces within the brain, filled with cerebrospinal fluid.

Explanation:

cerebrospinal fluid

A clear fluid, similar to blood plasma, that fills the ventricular system of the brain and the subarachnoid space surrounding the brain and spinal cord.

Ventricle of brain

The ventricles of the brain are a communicating network of cavities filled with cerebrospinal fluid (CSF) and located within the brain parenchyma. The ventricular system is composed of 2 lateral ventricles, the third ventricle, the cerebral aqueduct, and the fourth ventricle.