Diencephalon is the posterior part of the forebrain, which includes the thalamus and the hypothalamus. The term is also used for the region of the vertebrate neural tube which gives rise to the above mentioned structures. The diencephalon is almost completely hidden from the surface of the brain.


It is a large mass of grey matter that lies on either side of the third ventricle. It serves as a relay station on the sensory fibers to the cerebral cortex.


It forms part of the lateral wall and the floor of the third ventricle and is composed of the following structures from before backwards:

  • Optic chiasma
  • Tuber cinerium
  • Infundibulum
  • Mamillary bodies
  • Posterior perforated substance