The brain is a component of the central nervous system.

During development the brain can be divided into five continuous parts. From rostral (or cranial) to caudal they are:

• Telencephalon (cerebrum) - develops into the large cerebral hemispheres; their surface contains elevations (gyri) and grooves (sulci) and is partially separated by a deep longitudinal fissure; the cerebral hemispheres fill the cranial cavity above the tentorium cerebelli and are subdivided into lobes based on their position.

• Diencephalon - a part, which is hidden from view in the adult brain by the cerebral hemispheres; consists of the thalamus, hypothalamus, and other related structures, and classically is considered to be the most rostral part of the brainstem. (However, in common use today, the term brainstem usually refers to the midbrain, pons, and medulla.)

• Mesencephalon (midbrain) - the first part of the brainstem seen when an intact adult brain is examined, and is at the junction between and located in both the middle and posterior cranial fossae.

• Metencephalon - gives rise to the cerebellum (consisting of two lateral hemispheres and a midline part in the posterior cranial fossa below the tentorium cerebelli) and the pons (anterior to the cerebellum, a bulging part of the brainstem in the most anterior part of the posterior cranial fossa against the clivus and dorsum sellae).

• Myelencephalon (medulla oblongata) - the most caudal part of the brainstem, which ends at the foramen magnum or the uppermost rootlets of the first cervical nerve and to which cranial nerves VI to XII are attached.