The skull is a bone protective cavity for the brain. The skull is composed of three types of bone: cranial bones, facial bones, and ear ossicles. Two parts are more prominent: the cranium (pl.: craniums or crania) and the mandible. In humans, these two parts are the neurocranium (braincase) and the viscerocranium (facial skeleton) that includes the mandible as its largest bone. The skull forms the anterior-most portion of the skeleton and is a product of cephalisation—housing the brain, and several sensory structures such as the eyes, ears, nose, and mouth. In humans, these sensory structures are part of the facial skeleton.