As explained above the subthalamic nucleus which has traditionally been described as a part of the subthalamic region is now grouped functionally with the basal nuclei which are considered.
The subthalamic nucleus is shaped like a biconvex lens. It lies between the thalamus above, and the substantia nigra below (Figs. 13.2, 13.28). The upper end of the red nucleus is close to it. The nucleus is closely related to the zona incerta, the fascicularis lenticularis intervening between the two.
The fibres connecting the subthalamic nucleus to the globus pallidus form a bundle called the subthalamic fasciculus which passes through the internal capsule.