"Brain juice" redirects here. For the R. L. Stine "Goosebumps" book, please see Brain Juice. Cerebrospinal fluid (CSF), Liquor cerebrospinalis, is a clear, colorless bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord. In essence, the brain "floats" in it. The CSF occupies the space between the arachnoid mater (the middle layer of the brain cover, meninges), and the pia mater (the layer of the meninges closest to the brain). It constitutes the content of all intra-cerebral (inside the brain, cerebrum) ventricles, cisterns, and sulci (singular sulcus), as well as the central canal of the spinal cord...