SKULL, the skeleton of the head; the bony or cartilaginous framework of the head in vertebrates; a superior expansion of the verte bral column. Its shape differs in various ani mals. In man it is somewhat ovoid, the larger portion being at the top (the dome) ; and the whole is composed of flat and irregular bones eight bones -enclosing the cranial cavity and 14 forming the face. The skull rests and nods upon the first vertebra (atlas). It also rests upon a tooth-like process (odontoid process) of the axis, or second bone of the spinal column, which projects upwards through the atlas and forms a pivot or swivel, upon which the head rotates, the atlas also turning with it. The pre ponderance of the cranial portion of the skull over the face portion is most pronounced in man, because of the higher development of the brain. The cranial portion (cranium) is composed of the occipital, frontal, sphenoid and ethmoid bones, and the two parietal and temporal bones. These bones are united either by sutures (dovetail joints) or beveled edges.
The upper bones of the skull of a baby do not usually unite until months after birth, their condition alloWing the brain to grow. The dovetail joints later in life fasten these bones together very firmly. Thisjointure, together with the strong buttresses in the temporal bones and the tie-beam function of the sphenoid, adapts an adult for carrying considerable weight upon the head without injury. If the upper cranial bones of a baby are united at birth or soon after, the child is usually an imbecile or idiot. The tissue of the flat bones of the skull is arranged in layers; the outer one was likened by the ancients to wood, the middle one to leather, and the inner one to glass. The cranial cavity contains the brain and proximalportions of the cranial nerves. See BRAIN; CRANIAL
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. The principal opening of the skull is the foramen magnum for the transmission of the beginning of the spinal cord, the spinal ac cessory nerves, and the vertebral arteries. Other openings to the orbits, the interior of the temporal bones, etc., transmit the optic, audit ory, and other nerves, as well as blood-vessels, and are so arranged that these nerves and ves sels are not easily injured.
The bones of the face are the inferior maxil lary, and the vomer, the two nasal, superior maxillary, lacrimal, malar, palate, and inferior turbinated. The inferior maxillary, or lower jaw, forms the chin (a distinctive feature of man), moves in mastication and speech, and is joined to the temporal bone by a ball-and-socket joint. The lacrimal bones are small bones form ing part of the inner wall of the orbit, one of the principal openings in the face. The malar bones are the cheek-bones. The palate-bones assist in the formation of the outer wall of the nose, the roof of the mouth, and the floor of the orbit. The nasal bones form the bridge of the nose; the vomer forms part of the septum of the nose, separating one nasal cavity from the other. The superior maxillary bones (maxilla, the jawbone) form the upper jaw and a large part of the roof of the mouth, the outer wall of the nasal fosse, and the floor of the orbit. The inferior turbinated bones ex tend horizontally along the outer wall of the nasal fosses. The principal external openings of the skull in the face portion are the orbits, the mouth, and the nasal opening; in the cranial portion, the foramen magnum, and the external auditory canal. See ANATOMY; HEAD; ME