This shows  the 3 primordial areas. 

Epithalamus: Pa and Habenula

Ventral thalamus: reticular nucleus and zonaincerta

Dorsal thalamus:  thalamus “proper”

The dorsal thalamus is further divided into the Principal nuclei and the intralaminar nu. 

The principal nuclei are the major relay of information to the cerebral cortex.  They have reciprocal connections with specific, restricted areas of cortex. 

The intralaminar nuclei also project to cortex, although in a less well organized manner, and project strongly to the striatum as well.