medulla

The inner core of certain organs or body structures, such as the marrow of bone.

The medulla oblongata.

The pith in the stems or roots of certain plants.

The central portion of a thallus in certain lichens and red or brown algae.

The semi-fluid endosarc of a protozoön.

In anatomy and zoology: Marrow. [Little used.]

The so-called spinal marrow; the spinal cord, or central axis of the nervous system; the myelon: more fully called medulla spinalis.

The hindmost segment of the brain, continuous with the spinal cord; the afterbrain or metencephalon; the oblongata: more fully called medulla oblongata.