Formation of Compact Bone in a Human
Transverse section of femur of a human embryo about eleven weeks old. Labels: a, rudimentary Haversian canal in cross sections; b, in longitudinal section; c, osteoblast; d, newly formed osseous substance of a lighter color; e, that of greater age; f, lacunae with their cells; g, a cell still united to an osteoblast.
Baker, W. Morrant & Harris, Vincent Dormer Kirkes' Hand-book of Physiology, 13th ed. (Philadelphia: P. Blakiston's Son & Co., 1892) 71