Page 276 - Atlas of Histology with Functional Correlations

collagen fibers of the periosteum (3, 10) are in continuity with the fibers of the

embryonic connective tissue of adjacent marrow cavities (3) and with collagen
fibers within the trabeculae of bone (7, 11).

Osteoblasts (6, 10) deposit the bony matrix and are in linear arrangement
along the developing trabeculae of bone (7, 11). Osteoid (14), the newly
synthesized bony matrix, is seen on the margins of bony trabeculae. The

osteocytes (5) are located in lacunae of the trabeculae (7, 11). The
multinucleated osteoclasts (13) resorb and remodel bone during its formation.

Although collagen fibers in the bony matrix are obscured, the continuity with
embryonic connective tissue fibers in the marrow cavities may be seen at the

margins of numerous trabeculae (3).

Formation of new bone is not a continuous process. Inactive areas appear
where ossification has temporarily ceased. Osteoid and osteoblasts are not
present in these areas. In some primitive marrow cavities, fibroblasts
differentiate into osteoblasts (3, 10).

FIGURE 7.24 ■ Intramembranous ossification: developing mandible
(decalcified bone, transverse section). Stain: Mallory-Azan. Low magnification.

FIGURE 7.25 | Intramembranous Ossification:

Developing Skull Bone

A higher-power photomicrograph illustrates the development of skull bone by

the process of intramembranous ossification. The connective tissue periosteum
(5) surrounds the developing bone and gives rise to the osteoblasts (1, 6) that
form the bone (7). Osteoblasts (1, 6) are located along the developing bony

trabeculae (3). Trapped within the formed bone (7) and the bony trabeculae (3)
are the osteocytes (2) in their lacunae. Also associated with the bony trabeculae

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