Medullary bone

Cross section of the tibiotarsus of a laying hen (PAS): overview

The micrograph above demonstrates a cross section through the middle part of the tibiotarsus of a laying hen. In hatching season, under influence of estrogen, the development of medullary bone will start in female birds. Medullary bone serves as a source of easily reabsorbable calcium which is needed for the formation of the egg shell. Medullary bone is being formed against the inside of the compact bone of especially long non-pneumatized bones such as the femur and the tibiotarsus. It is a non-structural type of woven bone that exists of thin unorganized bony spicules which gives it a spongy appearance.