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.
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 tentorium separates the cerebrum from the cerebellum. The infratentorium (posterior fossa) is the region below the tentorium that contains the brain stem, cerebellum, and fourth ventricle. The supratentorium is the region above the tentorium and denotes the region that contains the cerebrum.