Definition of "bone marrow" [bone marrow]

• The soft, fatty, vascular tissue that fills most bone cavities and is the source of red blood cells and many white blood cells. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "From the bone marrow they move to the thymus, a butterfly-shaped organ situated over the heart in the center of the upper chest, right behind your sternum, or breastbone."
• "Normally, our bone marrow and thymus produce millions of T cells, which are the foot soldiers that work diligently to serve the immune system."
• "When researchers placed bone marrow in mice that expressed additional copies of the Fc receptor gene, those mice did not develop autoimmune disease."