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The parietal bone is ossified in membrane from a single center, which appears at the parietal eminence about the eighth week of fetal development. Ossification gradually extends in a radial manner from the center toward the margins of the bone; the angles are consequently the parts last formed, and it is here that the fontanelles exist.
The parietal eminence (parietal boss, parietal tuber, parietal tuberosity) is a convex, smooth eminence on the external surface of the parietal bone of the skull.It is the site where intramembranous ossification of the parietal bone begins during embryological development.
The calvaria is made up of the superior portions of the frontal bone, occipital bone, and parietal bones. [1] In the human skull, the sutures between the bones normally remain flexible during the first few years of postnatal development, and fontanelles are palpable. Premature complete ossification of these sutures is called craniosynostosis.
The endocranium, the bones supporting the brain (the occipital, sphenoid, and ethmoid) are largely formed by endochondral ossification. Thus frontal and parietal bones are purely membranous. [12] The geometry of the skull base and its fossae, the anterior, middle and posterior cranial fossae changes rapidly.
The following bones develop in humans via Intramembranous ossification: [3] Flat bones of the face; Most of the bones of the skull; Clavicles; Other bone that formed by intramembranous ossification are: cortices of tubular and flat bones as well as the calvaria, upper facial bones, tympanic temporal bone, vomer, and medial pterygoid process. [4]
The flat bones are: the occipital, parietal, frontal, nasal, lacrimal, vomer, sternum, ribs, and scapulae. [1] These bones are composed of two thin layers of compact bone enclosing between them a variable quantity of cancellous bone, [1] which is the location of red bone marrow. In an adult, most red blood cells are formed in flat
1 occipital bone; 2 parietal bones; 1 sphenoid bone; 2 temporal bones; The ossicles (three on each side) are usually not included as bones of the neurocranium. [6] There may variably also be extra sutural bones present. Below the neurocranium is a complex of openings and bones, including the foramen magnum which houses
Endochondral ossification is the formation of long bones and other bones. This requires a hyaline cartilage precursor. There are two centers of ossification for endochondral ossification. The primary center. In long bones, bone tissue first appears in the diaphysis (middle of shaft). Chondrocytes multiply and form trebeculae.