LM of bone marrow obtained via needle biopsy from the medullary cavity of the iliac crest. In the adult, bone marrow is the major organ of hematopoiesis. It produces erythrocytes, granular and agranular leukocytes, and platelets. This highly cellular, richly vascularized connective tissue consists of small hematopoietic stem cells (He) and larger adipocytes (fat cells, FC). Bony trabeculae (Bo) are closely associated with the marrow. Abundant thin-walled venous sinusoids (VS) provide the main exit route for newly formed blood cells that move directly into circulation. 180×. H&E.