Ventral thalamus , Thalamus ventralis

Counted as the midbrain (diencephalon).

The subthalamus area is located in part:

1/ sandwiched between the outside of the thalamus and the capsula interna in the form of the reticular thalamus nucleus

and partly and above all

2/ sandwiched between the underside of the thalamus and the hypothalamus.
Here lies the subthalamic nucleus (nucl.subthalamicus), zona incerta, the Forelian fields and the return connections between the striatum-globus pallidus and the thalamus.

The apparently peculiar distribution of the subthalamus is due to the fact that the very rapidly growing predisposition of the dorsal thalamus during fetal development squeezes and displaces the predisposition of the subthalamus both in lateral (1/) and ventral (2/) directions.