What is the X in X-mas?
habenula ha·ben·u·la (hā-běn'yə-lə)
n. pl. ha·ben·u·lae (-lē')
The stalk of the pineal gland. No longer in technical use.
A circumscript cell mass embedded in the posterior end of the medullary stria of the thalamus, from which it receives most of its afferent fibers. Also called habena, pedunculus of pineal body.