on the lateral side of the brain case above the level of the zygomatic arch is a shallow space called the temporal fossa the temporal fossa articulates with the mandibular condyle of the mandible or jaw bone bones of the brain case the brain case contains and protects the brain the interior space that is almost completely occupied by the brain is called the cranial cavity the brain case consists of eight bones these include the paired parietal and temporal bones plus the unpaired frontal ethmoid sphenoid and occipital bones the parietal bone forms most of the upper lateral side of the skull these are paired bones with the right and left parietal bones joining together at the top of the skull each parietal bone is also bounded anteriorly by the frontal bone and posteriorly by the occipital bone and inferiorly by the temporal bone the temporal bone forms the lower lateral side of the skull the temporal bone contains some important landmarks these include the external acoustic meatus the internal acoustic meatus the mandibular fossa and the styloid process the external acoustic meatus or ear canal is the large opening located on the lateral side of the skull that is associated with the ear the internal acoustic meatus is an opening located inside the cranial cavity on the medial side of the petrus ridge this connects the middle ear and inner ear cavities of the temporal bone the mandibular fossa is a deep oval-shaped depression located on the external base of the skull just in front of the external acoustic meatus the mandible or lower jaw joins with the skull at this site as part of the temporal mandibular joint or tmj the temporal mandibular joint allows for movement of the mandible during opening and closing of the mouth the styloid process is posterior to the mandibular fossa on the external base of the skull it is an elongated and downward bony projection called the styloid process this is called the styloid process because it resembles a stylus or writing pen this structure serves as an attachment site for several small muscles and ligaments that support the hyoid bone of the neck the frontal bone is the single bone that forms the forehead the frontal bone is thickened just above the supraorbital margin forming the rounded brow ridges the occipital bone is the single bone that forms the posterior skull and the posterior base of the cranial cavity on the base of the skull the occipital bone contains a large opening called the foramen magnum the foramen magnum allows for passage of the spinal cord as it exits the skull on either side of the foramen magnum is an oval-shaped occipital condyle these condyles form joints with the first cervical vertebrae and thus support the skull on top of the vertebral column the sphenoid bone is a single complex bone located at the center of the skull it serves as a keystone bone because it joins with almost every other bone of the skull inside the cranial cavity the right and left lesser wings of the sphenoid bone form the lip of a prominent ridge that marks the boundary between the anterior and middle cranial fossa the celotursica is located at the midline of the middle cranial fossa this houses the pea-sized pituitary gland the greater wings of the sphenoid bone extend laterally to either side away from the cela turcica where they then form the anterior floor of the middle cranial fossa the ethmoid bone is a single midline bone that forms the roof and lateral walls of the upper nasal cavity it also creates the upper portion of the nasal septum and contributes to the medial wall of the orbit of the eye within the nasal cavity the perpendicular plate of the ethmoid bone forms the upper portion of the nasal septum extending from each lateral wall are the nasal concha these are thin curved projections that extend into the nasal cavity in the cranial cavity the ethmoid bone forms a small area at the midline in the floor of the anterior cranial fossa this portion of the ethmoid bone consists of two parts the crista galli and the cripper form plates the crista galli which means rooster's comb or crest is a small upward bony projection located at the midline this structure functions as an anterior attachment point for one of the covering layers of the brain to either side of the crysta galley is the cribriform plate the cribriform plate is a small flattened area with numerous small openings termed the olfactory foramina small nerve branches from the olfactory areas of the nasal cavity pass through these openings to enter the brain the lateral portions of the ethmoid bone form the lateral nasal cavity wall and a portion of the medial orbit wall a suture is an immobile joint between adjacent bones of the skull the narrow gap between the bones is filled with dense fibrous connective tissue that unites these bones together the long sutures located between the bones of the brain case are not straight but instead follow irregular tightly

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