an image illustrating the four ventricles of the brain. these are large internal chambers filled with cerebral spinal fluid. the fluid is produced in the lateral ventricles and circulates until it is absorbed by the arachnoid layer (the middle meninx). CSF seems to act as a fluid cushion for the brain, but it also transports some substances into/out of the brain and maintains homeostasis of pressure around the brain. basically, it’s pretty important.