Substantia innominata

The substantia innominata (literally "unnamed substance") of Meynert is a stratum consisting partly of gray and partly of white substance, which lies below the anterior part of the thalamus and lentiform nucleus. It is part of the basal forebrain.

It consists of three layers, superior, middle, and inferior.


 * The superior layer is named the ansa lentiformis, and its fibers, derived from the medullary lamina of the lentiform nucleus, pass medially to end in the thalamus and subthalamic region, while others are said to end in the tegmentum and red nucleus.


 * The middle layer consists of nerve cells and nerve fibers; fibers enter it from the parietal lobe through the external capsule, while others are said to connect it with the medial longitudinal fasciculus.


 * The inferior layer forms the main part of the inferior stalk of the thalamus, and connects this body with the temporal lobe and the insula.