Which marrow is soft and fatty and found in the medullary cavity of long bones?

• A. Red marrow
• B. Spongy bone
• C. Compact bone
• D. Yellow marrow

Answer: (D)

In adult long bones, the medullary cavity houses yellow marrow, which is soft and fatty. Yellow marrow is made up largely of adipose tissue and serves as a fat storage reserve. Red marrow, by contrast, is hematopoietic and produces blood cells, and in adults it’s found mainly in flat bones and the ends of long bones rather than in the medullary cavity of the shaft. Spongy bone and compact bone are types of bone tissue, not marrow. So the description of a soft, fatty tissue in the medullary cavity of long bones points to yellow marrow.