The substantia innominata (literally "unnamed substance") of Meynert is a stratum in the human brain consisting partly of gray and partly of white substance, which lies below the anterior part of the thalamus and lentiform nucleus. The gross anatomical structure is called the anterior perforated substance because, to the naked eye, it appears to be perforated by many holes (which are actually blood vessels). It is part of the basal forebrain and includes the nucleus basalis.
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.