di·en·ceph·a·lon 
(dī′ĕn-sĕfə-lŏn′, -lən)
(dī′ĕn-sĕfə-lŏn′, -lən)n.
The posterior part of the forebrain that connects the midbrain with the cerebral hemispheres, encloses the third ventricle, and contains the thalamus and hypothalamus. Also called betweenbrain, interbrain.
[DI(A)- + ENCEPHALON.]
di·en·ce·phalic (-sə-fălĭk) adj.