substantia nigra morphology trait Any measurable or observable characteristic related to the shape, structure, color, or pattern of the layer of grey substance that separates the posterior parts of the cerebral peduncles (tegmentum mesencephali) from the anterior parts; it normally includes a posterior compact part with many pigmented cells (pars compacta) and an anterior reticular part whose cells contain little pigment (pars reticularis). Trait.ontology VT:0000836 locus niger morphology trait nucleus niger morphology trait midbrain morphology trait basal ganglion morphology trait