label: substantia nigra
label_lc: substantia nigra
description: "Predominantly gray matter midbrain structure lying dorsal to the crus cerebri and ventral to the midbrain tegmentum. It is divided into a dorsal, cellularly compact region known as the pars compacta and a more ventrally located, containing more loosely packed cells, the pars reticulata. The most lateral region of the reticulata is identified as the pars lateralis (MM)."