substantia nigra morphology trait locus niger morphology trait nucleus niger morphology trait VT:0000836 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 midbrain morphology trait basal ganglion morphology trait