The |skull| is one of the principle groups of bones in the human anatomy. The |skull| consists of twenty-six bones: eight bones form the cranium, which houses the |brain| and |ear| ossicles, plus fourteen facial bones, which form the front of the face, jaw, |nose|, |orbits|, and the roof of the |mouth|, three more bones make up the inner |ear| ossicles, and one more, the |hyoid bone|, is in the neck and is attached to the |temporal bone| by ~ligaments~ and anchors the tongue. The skull also contains a dental arcade of teeth, which are technically not bones, though they do share some of the compositional characteristics of bone tissue. Children may grow twenty deciduous (non-permanent) teeth, which will eventually fall out and be replaced by the permanent teeth (32 of them in the average adult). The bones of the |skull| include the |frontal bone| (which makes up the forehead and roof of the |orbits|), the |occipital bone| (which forms the back and base of the |skull|), two |parietal bones| (which form the roof and upper sides of the |skull|), and two |temporal bones| (which form the lower sides of the |skull| and house the inner |ear| ossicles). The lower rearmost part of each |temporal bone| is called the |mastoid process|, but because it is separated from the |temporal bone|, proper, by a suture, it is often considered a separate bone. The |sphenoid bone| forms the central base of the |skull| and spans the |skull| from side to side, the greater wings forming side plates of the |skull|.
The sections of the |ethmoid bone| are positioned between the |orbits|, forming the walls and roof of the |nasal cavity|, while the three middle |ear| ossicles (stapes, malleus, and incus) are located within the |temporal bones| on each side of the |skull|. The U-shaped |hyoid bone| is found in the neck, and is attached by ~ligaments~ to the |temporal bones|. In the face, the two maxillary bones form much of the |orbits|, |nose|, upper jaw and roof of the |mouth|, while the malar (zygomatic) bones form the cheeks. The |lachrymal bones| are located on the inner sides of the |orbits| and are attached to the ethmoid and maxillary bones. Within the |nasal cavity|, the vomer is located in the low center and forms the thin flat bone of the |nasal septum|, while two inferior urbinates form the lower sides of the cavity and two palate bones form the floor of the |nasal cavity| as well as the roof of the |mouth|. The |mandible| is the only movable part of the |skull|, forming the lower jaw and mounting the |teeth|.
The bones of the |skull|, with the exception of the |mandible|, are held together by very thin sutures, or seams, in which the |periosteum| of the individual bones interweave with each other, and are cemented by a fibrous, connective tissue. In the newborn, these sutures are not yet developed, with the bones being attached by ~cartilage~ which ossifies over time as the bones of the |skull| fuse together. The most evident external sutures of the cranium include the |coronal suture|, joining the frontal and |parietal bones|, the |sagittal suture|, joining the |parietal bones| to each other, the |lambdoid suture|, joining the occipital and |parietal bones|, the |squamous suture|, joining the temporal and |sphenoid bones| to the |parietal bone| on each side of the |skull|. The |pterion| is the short segment of the suture joining the squamous and |parietal bones|.
The bones of the |skull| also feature a number of ~sinuses~ (cavities) and foramina (the plural of ~foramen~, meaning hole or opening). Four pairs of ~sinuses~ flank the |nasal cavity| (and are therefore called paranasal ~sinuses~). Two are found in the maxillary bone, and are called |maxillary sinuses|. The |sphenoid bone| forms two paranasal ~sinuses~ called the sphenoids, and the |ethmoid bone| forms the two paranasal ~sinuses~ called ethmoids. Additionally, the |frontal sinuses| are located in the |frontal bone| just behind the roof of each |orbit|. The |foramen magnum| is a large, round opening in the base of the |skull| which admits the |spinal cord|, while at the base of each |temporal bone| is the |external auditory meatus|, which serve as the auditory canals. Just above each |orbit| in the |frontal bone| is a small notch or hole, called a |supraorbital foramen|, and just below each |orbit|, in the maxillary bone, is an |infraorbital foramen|. Two more openings, one on each side of the |skull|, can be found in the frontal ~processes~ of the malar (zygomatic) bones, and are called, therefore, zygomatofacial foramina. On each side of the |mandible|, just below the lower |canines|, are the mental foramina. These facial foramina serve to admit ~blood~ vessels and ~nerves~ through and into the bone.
The |teeth| are mounted in the maxillary bone and the |mandible|, and are brought together for chewing by the hinge-like motion of the |mandible| (the lower jawbone). An average adult will have thirty-two |teeth|, evenly arrayed on the |maxilla| and |mandible|.
