forebrain morphology trait diencephalon morphology trait Any measurable or observable characteristic related to the shape, structure, color, or pattern of the paired caudal parts of the prosencephalon from which the thalamus, hypothalamus, epithalamus and subthalamus are derived; these regions regulate autonomic, visceral and endocrine function, and process information directed to the cerebral cortex. Trait.ontology VT:0000830