The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself. It is pierced by a large oval aperture, the foramen magnum, through which the cranial cavity communicates with the vertebral canal.
The parietal bones are paired bones in the human skull which, when joined together, form the sides and roof of the cranium. The parietal bone is ossified in membrane from a single center, which appears at the parietal eminence about the eighth week of fetal life. The radial manner of ossification from the center toward the margins of the bone causes the fontanelles to exist.
The frontal bone is derived from neural crest cells and is ossified in membrane from two primary centers, one for each half, which appear toward the end of the second month of fetal life.
The paired temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum. The temporal bone supports the structures of hearing as well as allows the major vessels to traverse to and from the brain. The posterior branch of the middle meningeal artery passes under the temporal bone, and trauma to this bone often leads to bleeding, which can progress to epidural hematoma.
The ethmoid bone is a bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits. The ethmoid bone is one of the bones that make up the orbit of the eye. The ethmoid has three parts: the cribriform plate, the ethmoidal labyrinth, and the perpendicular plate.
The sphenoid is an unpaired cranial bone situated at the front middle of the skull in front of the temporal bone and basilar part of the occipital bone. The sphenoid bone is one of the seven bones that articulate to form the orbit. Its shape somewhat resembles that of a butterfly.
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