Drawing of the inside of the brain showing  the lateral ventricle, third ventricle, and fourth ventricle, cerebrum, choroid plexus, hypothalamus, pineal gland, pituitary gland, optic nerve, tentorium, cerebellum,  brain stem, pons, medulla, and spinal cord.
Figure 1. Anatomy of the inside of the brain, showing the pineal and pituitary glands, optic nerve, ventricles (with cerebrospinal fluid shown in blue), and other parts of the brain. The posterior fossa is the region below the tentorium, which separates the cortex from the cerebellum and essentially denotes the region containing the brain stem, cerebellum, and fourth ventricle.