Head
in anatomy, the skull, or cranium. Part of the head consists of an osseous ovoidal capsule for the protection of the brain. The face proper consists of the upper and lower jaws. The skull in old age becomes composite like the sacrum in the adult. The margins, or sutures, of the cranial bones, 22 in number excluding the hyoid bone, correspond to the articular processes in the trunk.
In youth the flat cranial bones are connected by a double lamina of cartilage; notwithstanding the junction of the margins, they grow by the increase of one cartilage and the ossification of the other. Like the arch in the movable vertebræ, we have the arch in the head; in the lower part there are bones physiologically connected with the head bones of the neck. There are three segments in the head: (a) The posterior, beginning from the cervical vertebræ below the occipital segment, consisting of a single bone, in reality four bones; a part of it lies in the base of the cranium at the back of the face, but the greater part extends up the back of the cranium. It consists of a ring, lateral sides, and an arch. (b) The anterior, 'consisting of the frontal and ethmoid bones. The only vestige here of the ver- HEALTH INSURANCE tebral foramen is the foramen cæcит. (c) The central segment; in the middle line below, and cut in two halves by the mœsial plane, is the sphenoid bone, but along with it are two bones, the temporal, attached to its outer portions or great wings, composing the basis of the arch completed by the two parietal bones.
These segments are divided by the lambdoidal sutures and coronal. The head is divided into a base and a vault, or calvarium; the inner aspect is called the cerebral, the other the superficial, external, etc., aspect. The bone on the outside of the cranium is not so dense as it is on the inside, in accordance with a law of construction in all animal and vegetable bodies, a law of part, and a law of place. Some anatomists count four segments, the two temporal bones constituting the fourth. The vertebrata have a head homologous in its anatomy with that of man. That of the Annulosa is homologous in functions, but not in parts. The cephalopodous and gasteropodous mollusks have heads, the Conchifera, sometimes called Acephala, want them. Most animals of lower organization than these are destitute of heads.