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.