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.