Facial Bones

Sun, 11 Oct 2009 20:08:08 +0100

Okay, lets talk about the facial bones now.
The fourteen bones of the skull not in contact with the brain are called the facial bones.
    There are two maxillae unite at the midline to form the upper jaw, which supports the upper teeth. Incisors, canines, premolars, and molars are contained in sockets, or alveoli, within the alveolar process of the maxilla. The palantine process, a horizontal plate of the maxilla, forms the greater portion of the hard plate, of roof of the mouth. The incisive foramen is located in the anterior region of the hard plate behind the incisor teeth. An infraorbital foramen is located under each orbit and serves as a passageway for the infraorbital nerve and artery to the nose. A final opening within the maxilla is the inferior orbital fissure. It is located between the maxilla and the greater wing of the sphenoid and is the external opening for the maxillary branch of the trigeminal nerve and infraorbital vessels. The large maxillary sinus located within the maxilla is on of the four paranasal sinuses.

    The L-shaped palatine bones form the posterior third of the hard plate, a portion of the orbits, and a partof the nasal cavity. The horizontal plates of the palatines contribute to the formation of the hard plate. On the hard plate of each palatine bone is a large greater palatine foramen, which permits the passage of the greater palatine nerve and descending palatine vessels. Two or more smaller lesser palatine foramina are positioned posterior to the greater palatine foramen. Branches of the lesser palatine nerve pass through these openings.

    The two zygomatic bones form the cheek-bones of the face. A posteriorly extending zygomatic process of this bone unites with that of the temporal bone to form the zygomatic arch. The zygomatic bone also forms the lateral margin of the orbit. A small zygomaticofacial foramen, located on the anterolateral surface of this bone, allows passage of the zygomatic nerves and vessels.

    The small lacrimals are thin bones that form the anterior part of the medial wall of each orbit. Each hasa lacrimal sulcus, a groove that helps to form the nasolocrimal canal. This opening permits the tears of the eye to drain into the nasal cavity.

    The small, rectangular nasal bones join in the midline to form the bridge of the nose. The nasal bones support the flexible cartilaginous plates, which are a part of the framework of the nose. Common facial injuries include fractures of the nasal bones or fragmentation of the supporting cartilages.

    The two inferior nasal conchae are fragile, scroll-like bones that project horizontally and medially from the lateral walls of the nasal cavity. They extend into the nasal cavity just below the superior and middle nasal conchae, which are part of the ethmoid bone. The inferior nasal conchae are the largest of the three conchae, and, like the other two, are covered with mucous membranes to warm, moisten, and cleanse inhaled air.

    The vomer is a thin, elongated bone that forms the lower part of the nasal septum. The vomer, along with the perpendicular plate of the ethmoid, supports the septal cartilage to complete the nasal septum.

    The mandible, or lower jawbone, is attached to the skull by a temporomandibular articulation, and is the only movable bone of the skull. Several muscles that close the jaw extend from the skull to the mandible. The mandible of an adult supports sixteen teeth within the alveoli, which occlude with those of the maxilla. The horseshoe-shaped front and horizontal lateral sides of the mandible are referred to as the body. Extending vertically from the posterior part of the body are two rami. Each ramus has a knob-like condyloid process, which articulates with the mandibular fossa of the temporal bone, and a pointed coronoid process for the attachment of the temporalis muscle. The depressed area between these two processes is the mandibular notch. The angle of the mandible is where the horizontal body and vertical ramus meet at the corner of the jaw. Two sets of foramina are found on the mandible: the mental foramen on the lateral side below the first molar and the mandibular foramen on the medial surface of the ramus. The mental nerve and vessels pass through the mental foramen and the inferior alveolar nerve and vessels are transmitted through the mandibular foramen.

    The hyoid bone is U-shaped and is located in the neck, just superior to the larynx. The hyoid is unique in that it does not attach directly to any other bone but is suspended from the styloid process of the skull by the stylohoid muscles and ligaments. The hyoid has a body, two lesser cornua extending anteriorly, and two greater cornua, which project posteriorly to the stylohoid ligaments. Several neck and tounge muscles attach to the hyoid bone. The hyloid may be palpated by placing a thumb and a finger on either side of the upper neck under the lateral portions of the mandible and firmly squeezing medially.

    Three small, paired auditory ossicles, the malleus, incus, and stapes, are located within the cavities of the middle ears in the petrous part of the temporal bones. These bones transfer and amplify sound impulses through the middle ear.

facial-bones

Facial Bones