Definition of diencephalon in US English:



  • The caudal (posterior) part of the forebrain, containing the epithalamus, thalamus, hypothalamus, and ventral thalamus and the third ventricle.

    Compare with telencephalon
    • ‘Eye development in zebrafish first becomes morphologically obvious at the 6 somite stage, the time at which the optic lobes evaginate from the diencephalon.’
    • ‘From previous anatomical data, we hypothesize that the level of such actions is suprametameric, with strong implication of the diencephalon and cerebral cortex.’
    • ‘The latter includes the diencephalon; mesencephalon, or midbrain; pons; and medulla oblongata.’
    • ‘The neurohypophysis, or posterior pituitary, is derived from an evagination of the infundibular portion of the diencephalon of the brain.’
    • ‘The internal capsule and corona radiata have been exposed by removal of the corpus callosum, caudate nucleus, and diencephalon.’


Late 19th century: from di- ‘across’ + Greek enkephalos ‘brain’.