The stria medullaris (SM), (Latin, furrow and pith or marrow) is a part of the epithalamus and forms a bilateral white matter tract of the initial segment of the dorsal diencephalic conduction system (DDCS).

The SM emerges as a bilateral compact fascicle just posterior to the anterior commissure, where it converges with the fornix and stria terminalis.

The medial SM fibers, on the other hand, flex inwards towards the pineal gland's base, crossing to the opposite side and terminating in the contralateral habenula.

The SM primarily gathers fibers from various brain regions, including the frontal, septal, striatal, and hypothalamic areas, and conveys information to the lateral and medial habenulae.

The SM, in conjunction with the habenula, has been identified as a potential therapeutic target for deep brain stimulation in the treatment of intractable depression.