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Frontal


Type

flat

Description

The frontal bone is a partial bowl shaped bone consisting of two parts: superiorly an internally concave vertical portion termed the squama, and inferiorly a horizontal plate of bone forming the roofs of the orbits. The bone has a smooth external surface, while its internal surface consists of variable shallow impressions from meningeal vessels and scattered foramina for diploic vessels. The squamous portion of the bone is thick. It consists of internal and external laminae of compact bone sandwiching a layer of spongy bone or diploe. Near the anterior, inferior midline the spongy bone is absent between the external and internal laminae and in its place are variably sized spaces - the frontal sinuses. The orbital plate consists of only a thin plate of compact bone, which is often so thin it is translucent.

Etymology

This word comes from the Latin words frons meaning front and frontis referring to the forehead or brow. The word denotes something anterior or a relation to the forehead or brow. The frontal bone was first described by Galen.

Articulations

The frontal bone articulates with twelve bones: the sphenoid, the ethmoid, both parietals, both nasals, the two maxillae, both lacrimals, and the two zygomatic bones. The most extensive articular surface is the denticulate to serrate border forming the frontoparietal or coronal suture at the posterosuperior margin. The borders forming the articular surfaces with the other above-mentioned bones are also denticulate in nature.

Ossification

The frontal bone ossifies intramembranously from two primary centers that appear during the eighth week of embryonic life. These centers form above each superciliary arch. Bone formation extends superiorly, inferiorly, and posteriorly from these centers to form the squama, nasal portions, and orbital plates, respectively. The two centers remain separate until about the eighth year. Complete fusion of the two halves occurring between the tenth and twelfth year. Sometimes a suture, the metopic, remains throughout adult life between the two halves of the frontal bone. Near the end of the first year of life nasal epithelium invades the bone initiating the formation of the frontal sinus. By approximately the eighth year they have become significant chambers, but do not attain their full size until full maturity. During the twelfth year, a secondary ossification center appears near the inferior midline. This center forms the nasal spine of the frontal bone.

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