Names and Locations of the Cranial Bones
Anatomy of Cranial Sutures and Markings
Names and Locations of the Cranial Sutures
Many other markings are found in cranial bones. For example, depressions in the parietal bones support blood vessels in the cranium. Depressions and projections in the temporal bones connect with the jawbone and allow the jaw to move up and down, and attachments for neck muscles allow the head to move.
Bones of the Face, Auditory Ossicles, and Hyoid Bone
Bones of the Face
The two nasal bones are small and elongated. They make up the bridge of the nose. The two maxillary bones together shape the upper jawbone. All other facial bones except the mandible (the lower jawbone) articulate with the maxillae. Each maxillary bone holds a sinus, and each features an alveolar process that holds the sockets (alveoli) for teeth of the upper jaw. Most of the hard palate that makes up the roof of the mouth is formed by the fused palatine processes, projections of each maxillary bone.
The two zygomatic bones are known as the cheekbones. They give cheeks their rounded shape and make up the bottom of the orbits, also called eye sockets, and form part of the orbits' outer wall. The term orbit may be either the bony socket or the contents of the socket. A zygomatic process, or marking, projects to the rear of each zygomatic bone, directly above the ear opening. Connected to a companion protrusion or process from each temporal bone, these processes form the zygomatic arch on each side of the face.
Mandibles are the largest facial bones and are the only moveable skull bones. The mandible includes a wide, curved portion, called the body, and a perpendicular section, called the mandibular ramus, on each side of the body. Each ramus features a bony projection (an outgrowth from the bone). that articulates with the temporal bone; together these form the temporomandibular joint. A jaw muscle, the temporalis, attaches to another process on the mandible, the coronoid process. An alveolar process along the mandible body holds sockets for the lower teeth.
The smallest facial bones are the two lacrimal bones. Thin and curved, the lacrimals are located behind and beside the nasal bones. They form part of the middle walls of the orbits. The two palatine bones form the rear of the hard palate, which separates the nasal and oral cavities. Palatine bones also contribute to parts of the nasal cavity and a small section of the orbits.
The inferior nasal conchae form part of the side walls of the nasal cavity. The two bones sit below the superior and middle conchae that are part of the ethmoid bone. Like those structures, the inferior nasal conchae increase surface area in the nose and help filter inhaled air. Finally, the vomer makes up the bottom rear portion of the nasal septum, the partition between the nostrils. The septum consists of the vomer articulated with a plate of the ethmoid bone, together with attached cartilage.A few other bones are associated with the skull in addition to the facial and cranial bones. Three auditory ossicles attach to one another in each middle ear. An auditory ossicle is a tiny bone that fits with the other two auditory ossicles, which together transmit sound wave vibrations from the tympanum, or eardrum, to the inner ear. Human ears have three ossicles: the malleus (hammer), incus (anvil), and stapes (stirrup).
Cranial Cavities and Sinuses
The eight cranial bones that make up the human skull house many cavities or contained spaces. The largest is the cranial cavity, which contains the brain. Three depressions, or fossae (anterior, middle, and posterior), form the interior floor, providing room for the brain and surrounding fluid. A ridge called the crista galli is located in the center of the anterior fossa, in the ethmoid bone. The crista galli is the attachment spot for the dura mater, the outermost of three meninges, which are membranes that protect the brain.
The paired orbits, or eye sockets, are skull cavities formed by several bones. The frontal and sphenoid bones frame each orbital roof, and the sphenoid and zygomatic bones compose the lateral (outer) orbital walls. The two maxilla (plural maxillae) bones make up each orbital floor, and the lacrimal, ethmoid, and palatine bones together form each medial (inner) orbital wall. Orbits are not completely round but rather are cone-shaped, tapering toward the back. Much of the eye is contained within its orbit, where it moves or orbits freely, which is the source of the structure's name. The orbital bones provide protection as well as attachment points for muscles that move the eye. Lacrimal (tear) glands, blood vessels, fat, and nerves are also held within orbits.Other skull cavities include the middle- and inner-ear cavities, buccal (or oral) cavity, nasal cavity, and paranasal sinuses. The middle-ear cavities contain the auditory ossicles. The buccal cavity forms the mouth. It is framed by the maxillae and the mandible—the jaws—and is separated from the nasal cavity by the palate. Like the orbits, the nasal cavity is composed of several bones. The frontal, nasal, sphenoid, and ethmoid bones frame the nasal cavity roof. The lateral walls are formed by the ethmoid, inferior nasal concha, lacrimal, and palatine bones. The maxilla and palatine combine to form the nasal cavity floor and side walls, as well as the hard palate at the roof of the mouth. The paired maxillae form the maxillary arch, which holds the upper row of teeth in place. The vomer and ethmoid bones make up the rigid part of the septum that divides the nasal cavity.