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Bone marrow; the spinal cord.

Greek muelos, marrow.

Terms that refer to bone marrow include myeloma, a malignant tumour of it; myelofibrosis, the replacement of bone marrow by fibrous tissue in some diseases; myelocyte, a cell of the bone marrow that develops into a granulocyte, a type of white blood cell; and myelin, a whitish insulating sheath around many nerve fibres, so named because it resembles marrow.

Myelo‑ came to refer to the spinal cord because of the concentration of grey matter and nerve fibres associated with it. Examples include myelitis, inflammation of the spinal cord; myelopathy (Greek patheia, suffering), a disease of it; and myelography, x-ray examination of the spinal canal inside the cord by injecting a radio-opaque substance into it.

The adjective myeloid can refer either to bone marrow or to the spinal cord.

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