This image shows a portion of the network of trabeculae that form the primary spongiosa of a fetal skull. The surfaces of the trabeculae are covered by osteoblasts (Obl) which are actively secreting osteoid, the unmineralized bone matrix. The osteoid can be seen as a thin layer of unstained stained matrix located between the osteoblasts and the mineralized bone matrix (BM), which is darkly stained with iron hematoxylin. Osteocytes (Ocy) are seen within the trabeculae, where they reside in lacunae. Note the blood vessels (BV) around which the trabeculae of the primary spongiosa typically form. The nuclei located in the tissue between and around the trabeculae embryonic belong to mesenchyme cells, which are precursors to the cells of the connective tissue.

Stain = Iron hematoxylin

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