the central axis of some hairs, containing a column of large vacuolated and keratinized cells; the medullary portion is surrounded by the cortex.
me·dul·la of hair shaft
(mĕ-dŭl'ă hār shaft) The central axis of some hairs, containing a column of large vacuolated and keratinized cells; the medullary portion is surrounded by the cortex.