part of limbic system A set of midline structures surrounding the brainstem of the mammalian brain, originally described anatomically, e.g., hippocampal formation, amygdala, hypothalamus, cingulate cortex. Although the original designation was anatomical, the limbic system has come to be associated with the system in the brain subserving emotional functions. As such, it is very poorly defined and doesn't correspond closely to the anatomical meaning any longer. [BirnLex]. visceral brain forebrain ectoderm-derived structure organ system subdivision