Section V. A "TYPICAL" FLAT BONE
4-10. GENERAL STRUCTURE
Another category of bones consists of the flat bones. (See Figure 4-2.)
Figure 4-2. "Typical" flat bone section.
a. The flat bones have two layers of dense bony tissue, called tables. Thus,
there is an inner table and an outer table.
b. Generally, between the two tables is a layer of cancellous bony tissue.
(1) The spaces of this cancellous bony tissue are filled with red marrow. In
adults, the red marrow of the flat bones is the primary blood-cell forming area of the
(2) As with the cancellous tissue of the long bone, the cancellous tissue of
the flat bone is organized into trabeculae. The trabeculae are oriented in the same
directions as the lines of applied forces, much like the struts of a building.
(3) Adjacent to the nasal cavities, many flat bones are hollowed to form the
paranasal sinuses. These hollow spaces take the place of cancellous bony tissue. The
development of the mastoid bone is likewise formed by the extension of the air-filled
cavity of the middle ear into the mastoid bone.