Framework of the Skull
The bony framework of the head, called the skull, is subdivided into two parts: the cranium and the facial portion. Refer to Figures 3-5 through 3-8, which show different views of the skull, as you study the following descriptions. Color-coding of the bones will aid in identification as the skull is seen from different positions. Cranium This rounded chamber that encloses the brain is composed of eight distinct cranial bones. * The frontal bone forms the forehead, the anterior of the skull’s roof, and the roof of the eye orbit (socket). The frontal sinuses (air spaces) communicate with the nasal cavities (see Figs. 3-7 and 3-8). These sinuses and others near the nose are described as paranasal sinuses. * The two parietal bones form most of the top and the side walls of the cranium. * The two temporal bones form part of the sides and some of the base of the skull. Each one contains mastoid sinuses as well as the ear canal, the eardrum, and the entire middle and internal portions of the ear. The mastoid process of the temporal bone projects downward immediately behind the external part of the ear. It contains the mastoid air cells and serves as a place for muscle attachment. * The ethmoid bone is a light, fragile bone located between the eyes (see Fig. 3-7). It forms a part of the medial wall of the eye orbit, a small portion of the cranial floor, and most of the nasal cavity roof. It contains several air spaces, comprising some of the paranasal sinuses. A thin, platelike, downward extension of this bone (the perpendicular plate) forms much of the nasal septum, a midline partition in the nose(see Fig. 3-5 A) * The sphenoid bone, when seen from a superior view, resembles a bat with its wings extended. It lies at the base of the skull anterior to the temporal bones and forms part of the eye socket. The sphenoid contains a saddlelike depression, thesella turcica, that holds and protects the pituitary gland * The occipital bone forms the...
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