Two small hard irregular bones, but of considerable importance owing to their having within them the special organs of hearing. They are interposed between the occipital bones above, and the parietal and temporal bones below, and assist in forming the lateral walls of the cranium. They are the hardest bones in the skeleton, and from them project several bony processes. One, the external auditory canal, communicates with the middle ear. Another, the styloid process, is a long thin piece of bone projecting downward and forward, and behind this is a larger rounded protuberance, the mastoid process, which is hollowed out into a number of small compartments connected with the middle ear. Another small process serves for attachment of the tongue bone, and is known as the hyoid process.