The brain consists of the cerebrum, the brainstem and the cerebellum. The brain consists of equal parts, cerebrum, midbrain and cerebellum. The cerebrum, brainstem, cerebellum, and spinal cord are covered by three membranes called meninges. In the brain, lesions exist in the cerebrum and cerebellum. Greek anatomist Erasistratus studied the brain and distinguished between the cerebrum and cerebellum. Aristotle did describe the meninges and distinguished between the cerebrum and cerebellum. The occipital bone overlies the occipital lobes of the cerebrum. The cerebral peduncles are the two stalks that attach the cerebrum to the brainstem. The tentorium separates the cerebrum (above) from the cerebellum (below). The basal ganglia form a fundamental component of the cerebrum. The prosencephalon or forebrain is the embryonic structure from which the cerebrum develops prenatally. The piriform cortex is part of the rhinencephalon situated in the cerebrum. He is credited with one of the first in-depth descriptions of the cerebrum and cerebellum. Both of these nuclei include projections to the motor cortex in the cerebrum. Archangelo Piccolomini of Rome was the first to distinguish between the cerebrum and cerebral cortex.