Histology of the developing mouse femur.

(A) E17 femur embedded in Unicryl and stained with hematoxylin/fast green shows spongy bone. Osteoblasts are aggregated in nodules and depose a calcified bone matrix in their surroundings. Arrows point to hematopoietic cells. (B) An abundant vascular conduit that follows the way of hypertrophied chondrocytes characterizes the newborn femur. (C) Proximal region of the femur from a young adult mouse containing spongy bone filled with bone marrow. Megakaryocytes form islands with erythroid and myeloid cells.