Figure 1-13. Sesamoid bone (the patella).
1-10. BONE FORMATION AND GROWTH
a. Fibrous-Membrane Formation (Intramembranous). The bones of the
cranium are formed from a fibrous membrane. In various portions of the membrane,
ossification centers develop. From these centers, tiny calcium spines radiate in all
directions; thus, a compact network of bone is formed centrally with peripheral areas
being much less compact. Between the radiating calcium columns, the osteoblasts
(bone-forming cells) construct the bone. Eventually, the periosteum is formed from the
membrane; the subperiosteal osteoblasts form the inner and outer tables of compact
bone; and the endosteal osteoblasts form the cancellous bone. The bone marrow
occupies the spaces within the cancellous bone (diploe). The bones of the cranium are
not completely ossified at birth and the membranous areas are called fontanelles. See
Figure 1-14 for an illustration of an infant's skull showing anterior and posterior
fontanelles.
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