2. outline, Medicine VISCEROCRANIUM.doc.pdf

OUTLINE 3. FACIAL BONES  MAXILLA Maxillae hold the upper teeth, both together form the upper jaw, and connect on the left and right with the zygomatic bones (cheek bones). Each assists in forming the boundaries of three cavities, namely, the roof of the...

OUTLINE 3. FACIAL BONES  MAXILLA Maxillae hold the upper teeth, both together form the upper jaw, and connect on the left and right with the zygomatic bones (cheek bones). Each assists in forming the boundaries of three cavities, namely, the roof of the oral cavity, the floor and lateral wall of the nasal cavity and the floor of the orbit. The maxilla also enters into the formation of two fossae, the infratemporal and pterygopalatine, and two fissures, the inferior orbital and pterygomaxillary. Each bone consists of a body and four processes, frontal, alveolar, zygomatic and palatine. The body (‘corpus maxillae’) The body is pyramidal in shape, and contains a large cavity, the maxillary sinus. It has base, nasal surface, apex and three surfaces - an anterior or facial, a posterior or infratemporal, a superior or orbital. Surfaces of the body The anterior surface is directed anterolaterally. Just above of the canine teeth is a depression, the canine fossa. Above the fossa is the infraorbital foramen, the end of the infraorbital canal; it transmits the infraorbital vessels and nerve. Medially, the anterior surface is limited by a deep concavity, the nasal notch, which with its fellow of the opposite side forms the anterior nasal spine. The infratemporal surface is convex, directed posterolaterally and forms part of the infratemporal fossa. It is separated from the anterior surface by the zygomatic process and by a strong ridge, extending upward from the socket of the first molar tooth. It is pierced about its center by the alveolar foramina, the apertures of the alveolar canals, which transmit the posterior superior alveolar vessels and nerves. At the lower part of this surface is a rounded eminence, the maxillary tuberosity. The orbital surface is a thin plate of bone, which forms the floor of the orbit. Immediately deep to this thin plate is the maxillary sinus. Near the middle of the posterior part of the orbital surface is the infraorbital groove, for the passage of the infraorbital vessels and nerve. The groove passes forward, and ends in an infraorbital canal. The canal opens into the anterior surface as the infraorbital foramen. The nasal surface presents a large, irregular opening, maxillary hiatus, leading into the maxillary sinus. Below the aperture is a smooth concavity which forms part of the inferior meatus of the nasal cavity, and behind it is a rough surface for articulation with the perpendicular plate of the palatine bone; this surface is traversed by a greater palatine groove. Groove is converted into a greater palatine canal by the perpendicular plate. In front of the opening of the sinus is deep groove, the lacrimal groove, which makes up about two-thirds of the cicrumference of the nasolacrimal canal. The rest of the canal is contributed by the lacrimal bone and inferior nasal concha; this canal opens into the inferior meatus of the nose and transmits the nasolacrimal duct, which transports tears from the orbit to the nasal cavity. More anteriorly is an oblique ridge, the conchal crest, for articulation with the inferior nasal concha. The frontal process ('processus frontalis; nasal process') Its lateral surface is divided by vertical anterior lacrimal crest, which is continuous below with the infraorbital margine of the body. The smooth area anterior to the anterior lacrimal crest merges below with the anterior surface of the body of the maxilla. Behind the crest, a vertical groove combines with one on the lacrimal bone to complete the lacrimal fossa. Its medial surface forms part of the lateral wall of the nasal cavity. A rough subapical area articulates with the ethmoidal bone, below this is the ethmoidal crest, the posterior end of which articulates with the middle nasal concha. The upper border articulates with the frontal bone and the anterior with the nasal; the posterior border is thick, and hollowed into a groove, which is continuous below with the lacrimal groove on the nasal surface of the body. The zygomatic process ('processus zygomaticus; malar process') The zygomatic process extends laterally to the zygomatic bone. In front it forms part of the anterior surface; behind, it is concave, and forms part of the infratemporal fossa; above, it is serrated for articulation with the zygomatic bone; while below, it presents the prominent arched border which marks the division between the anterior and infratemporal surfaces. The zygomatic process is the apex of the pyramid. The alveolar process ('processus alveolaris') The alveolar process of booth maxillae form the upper alveolar (dental) arch. The alveolar process forms the sockets and supporting bone for the maxillary teeth. These cavities dental alveoli are separated by interalveolar septa. They are eight in number, and vary in size and depth according to the teeth they contain. That for the canine tooth is the deepest; those for the molars are the widest, and are subdivided into minor cavities by interradicular septa; those for the incisors are single, but deep and narrow. The palatine process ('processus palatinus; palatal process') The palatine process, is horizontal and projects medially from the nasal surface of the bone. It forms a considerable part of the floor of the nose and the roof of the mouth. The superior surface of the palatine process is concave from side to side, smooth, and forms the greater part of the floor of the nasal cavity. It presents, close to its medial margin, the upper orifice of the incisive canal. The lateral border of the process is continuous with the body of the maxilla. The medial border is thicker in front than behind, and is raised above into a ridge, the nasal crest, which, with the corresponding ridge of the opposite bone, forms a groove for the reception of the vomer. The front of this ridge rises to a considerable height, and is named the incisor crest; it is prolonged forward into a sharp process, which forms, together with a similar process of the opposite bone, the anterior nasal spine. The posterior border is serrated for articulation with the horizontal part of the palatine bone (the transverse palatine suture). Its inferior surface is concave, and forms, with the palatine process of the opposite bone, the anterior three-fourths of the bony palate. The inferior surface displays palatine spines and palatine grooves for the transmission of the descending palatine vessels and nerve. The medial border articulates with the palatine process of the opposite bone, and forms the median palatine suture. The lateral border of the process is continuous with the rest of the bone. When the two maxillae are articulated, a tunnel-shaped opening, the incisive foramen, is seen in the middle line, immediately behind the incisor teeth. In this opening the orifices of two lateral canals are visible; they are named the incisive canals. On the under surface of the palatine process, a delicate linear suture, well seen in young skulls, may sometimes be noticed extending anterolaterally on either side from the incisive foramen to the interval between the lateral incisor and the canine tooth. The small part in front of this suture constitutes the premaxilla (os incisivum), which in most vertebrates forms an independent bone; it includes the whole thickness of the alveolus, the corresponding part of the floor of the nose and the anterior nasal spine, and contains the sockets of the incisor teeth. The maxillary sinus ('sinus maxillaris') The maxillary sinus is a large pyramidal cavity within the body of the maxilla: its apex extends into the zygomatic process and the base, medial wall, forms part of the lateral wall of the nasal cavity. Its walls are everywhere exceedingly thin, and correspond to the nasal, orbital, anterior, and infratemporal surfaces of the body of the bone. Its nasal wall, or base, presents a large, irregular aperture, communicating with the nasal cavity. In the articulated skull this aperture is much reduced in size by the following bones: the uncinate process of the ethmoid above, the ethmoidal process of the inferior nasal concha below, the vertical part of the palatine behind, and a small part of the lacrimal bone. It usually opens into the posterior part of the middle meatus of the nose, generally by two small apertures left between the above-mentioned bones. Usually only one small opening exists, near the upper part of the cavity; the other is closed by mucous membrane. The floor is formed by the alveolar process and part of the palatine process of the maxilla and the roof contributes the major part of the floor of the orbit. Anterior wall forms anterior, facial surface, and posterior wall is formed by infratemporal surface of the maxilla. The infraorbital canal usually projects into the cavity as a well-marked ridge extending from the roof to the anterior wall. On the posterior wall are the alveolar canals, transmitting the posterior superior alveolar vessels and nerves to the molar teeth. The size of the cavity varies in different skulls, and even on the two sides of the same skull. Changes produced in the maxilla by age At birth the transverse and anteroposterior diameters of the bone are each greater than the vertical. The frontal process is well-marked and the body of the bone consists of little more than the alveolar process, the teeth sockets reaching almost to the floor of the orbit. The maxillary sinus presents the appearance of a furrow on the lateral wall of the nose. In the adult the vertical diameter is the greatest reflecting the development of the alveolar process and enlargement of the sinus. In old age the bone reverts in some measure to the infantile condition; its height is diminished, and after the loss of the teeth the alveolar process is absorbed, and the lower part of the bone contracted and reduced in thickness. MANDIBLE The mandible is the largest, strongest and lowest bone in the face. It holds the lower teeth in place and articulates with the temporal bones of the skull at the temporomandibular movable synovial joints. It has a horizontally curved body that is convex forwards, and two broad rami, that ascend posteriorly. The junction of the posterior border of the ramus and the lower border of the body forms the prominent angle of the mandible. The body of mandible The body is U-shaped and has external and internal surfaces separated by upper and lower borders. Anteriorly, the external surface shows an inconstant faint median ridge, which indicates fusion of the halves of the fetal bone at the mandibular symphysis (symphysis menti). It is present at birth and begins to fuse in the first year of life, resulting in one mandible. Inferiorly, this ridge divides to enclose a mental triangle. Its base forms mental protuberance which eds on each side as a mental tubercle. The mental protuberance and mental tubercles constitute the chin. The mental foramen, from which the mental nerve and vessels emerge, is situated below either the interval between the premolar teeth, or the second premolar tooth. The external oblique line is a ridge of bone, which originates at the mental tubercle and sweeps upward and posteriorly to become the sharp anterior border of the ramus. A number of muscles of facial expresion are attached to the external surface of the mandible. The internal surface is divided by an oblique mylohyoid line, sharp and distinct near the molars, but faint in front. It extends from a point a centimetre from the upper border behind the third molar to the mental symphysis. To the mylohyoid line is attached mylohyoid muscle (and above its posterior end the superior pharyngeal constrictor, some fascicles of the buccinator, and the pterygomandibular raphe behind the third molar). Below this line is the slightly concave submandibular fossa which adjoins submandibular salivary gland. The area above the mylohyoid line widens anteriorly into a triangular sublingual fossa related to the sublingual gland. Above the mylohyoid line, medial to the molar roots, a rounded torus mandibularis – mandibular torus sometimes appears. In the midline of the body is a small elevation, often divided into upper and lower parts, the superior and inferior mental spines (or genial spine). The superior mental spine gives attachment to the genioglossus, and the inferior mental spine to the geniohyoid. The upper border, the alveolar part, contains 16 dental sockets, or the dental alveoli, for the roots of the lower teeth. It consists of lateral, or buccal (also called facial), and medial, or lingual, plates of bone joined transversely by interdental and interradicular septa. Interalveolar septa form individual sockets between the roots of adjacent teeth. Interradicular septa form individual sockets for the multirooted teeth. The roots cause on external surface of mandible bulges called alveolar yokes. The external surface of the alveolus adjacent to the molar teeth gives attachment to buccinator. If the teeth are lost, alveolar bone is resorbed and the mandibular canal and mental foramen come to lie nearer the superior border. The lower border of the body, the base, extends posterolaterally from the mandibular symphysis into the lower border of the ramus behind the third molar tooth. It can be palpated in its entirety just deep to the skin. Near the midline, on each side, is a rough digastric fossa that gives attachment to the anterior belly of the digastric muscle. The facial artery usually curls round the base of the mandible, sometimes making a shallow groove. The ramus of mandible The mandibular ramus is quadrilateral, and has two surfaces (lateral and medial), four borders (superior, inferior, anterior and posterior) and two processes (coronoid and condylar). The lateral surface is relatively fetureless and bears the oblique ridges in its lower part providing attachment for masseter (masseteric tuberosity). The medial surface presents, a little above centre, an irregular mandibular foramen, leading into the mandibular canal, curving down and forwards into the body. Anteromedially the foramen is overlapped by a thin, triangular, and tonguelike lingula. Attached to it is the sphenomandibular ligament. The mylohyoid groove runs downward and forward from the inferior border of the mandibular foramen, below the posterior part of the mylohyoid line. Occupying this groove are the nerve and vessels to the mylohyoid muscle. The medial surface of the ramus receives the medial pterygoid on the roughened area postero-inferior to the mylohyoid groove (pterygoid tuberosity). The thin superior border bounds the mandibular incisure (or the mandibular notch) surmounted in front by the somewhat triangular, flat coronoid process and behind by a strong condylar process. The inferior border of the mandibular ramus is continuous with the mandibular base. It is typically everted in males, but in females is frequently inverted. The anterior border is thin above where it is continuous with that of the coronoid process, and thicker below where it is continuous with the oblique line. The temporal crest is a ridge of bone on the internal surface of the ramus, paralelly to its anterior border. It runs down from the tip of the coronoid process to the third molar tooth where it divides into two ridges, lateral and medial. The retromolar fossa, is the depression between the lateral and medial ridges of temporal crest and the third molar. This landmark is extremly important in locating the site of injection for an anesthetic block of the inferior alveolar nerve. The posterior border, thick and rounded, extends from the condyle to the angle, being gently convex backwards above, and concave below. It is in contact with the parotid gland. The coronoid process is sharp and projects up slightly forwards. Its margins and medial surface are attachments for most of the temporalis. The condylar process consists of the head and neck. The head is covered by fibrocartilage and articulates with reciprocally shaped mandibular fossa of the temporal bone. It is convex in all directions with greater transverse dimension. Its lateral aspect is palpable in front of the auricular tragus. Below the head is the narrower neck. The neck’s anterior surface bears a rough pterygoid fovea which receives the lateral pterygoid. Its medial surface is related to the auriculotemporal nerve and maxillary artery. The mandibular canal The mandibular canal is the continuation of the mandibular foramen deep into the mandible. It runs obliquely inferiorly and anteriorly through the ramus and body just below the roots of the mandibular teeth with which it communicates by small canals. The canal ends at the midline. It carries the inferior alveolar nerve and vessels from which branches enter dental roots, periodontal sockets and septa. Between the roots of the first and second premolars, or below the second, the canal divides into mental and incisive parts. The mental canal swerves up, back and laterally to the mental foramen, and the incisive canal continues below the incisor teeth. INFERIOR NASAL CONCHA The inferior nasal concha is curved horizontal lamina in the lateral nasal wall. It has two surfaces, medial and lateral, two borders, superior and inferior and two ends, anterior and posterior. The medial surface is convex, and lateral is concave forming internal wall of the inferior nasal meatus. The superior border is divided into three regions; anterior articulating with the conchal crest of the maxilla, posterior articulating with the conchal crest of the palatine bone, and the middle part with three processes, variable in size and form. The lacrimal process is small and articulates with descending process from the lacrimal bone, it forms part of the nasolacrimal canal. Most posteriorly, a thin ethmoidal process articulates with uncinate process of the ethmoidal bone. In the midlle part of the superior border there is maxillary process. It curves inferolaterally to articulate with medial surface of the maxilla at the opening of the maxillary sinus. The inferior border is thick. LACRIMAL BONE The lacrimal bone is the smallest of the cranial bones. It lies anteriorly in the medial wall of the orbit. It has two surfaces, medial and lateral, and four borders, superior, inferior, posterior and anterior. The lateral (orbital) surface is divided by a vertical posterior lacrimal crest. Anterior to the crest there is vertical groove and the anterior edge of the groove meets the posterior border of the frontal process of the maxilla to complete the fossa for the lacrimal sac. The medial wall of the groove is prolonged by a descending process that contributes to the formation of the nasolacrimal canal by joining the maxilla and lacrimal process of inferior nasal concha. A part of the lateral surface behind the lacrimal crest extends inferiorly into the lacrimal hamulus, which, together with maxilla, completes the upper opening of the nasolacrimal canal. The anterior lacrimal border articulates with the frontal process of the maxilla, the posterior border with orbital plate of the ethmoid bone, the superior border with the frontal bone and the inferior border with the orbital surface of the maxilla.  NASAL BONE Two nasal bones are small, oblong, variable in size and form, and placed side by side between the frontal processes of the maxillae. They form the nasal bridge. Each nasal bone has two surfaces, external and internal, and four borders, superior, inferior, lateral and medial. The external surface is convex and internal concave. The superior border articulates with frontal bone. Thin inferior border is continuous with lateral nasal cartilage. The lateral border joins the frontal process of the maxilla and medial meet its fellow. VOMER The vomer is thin, flat and almost trapezoid. It forms posteroinferior part of the nasal septum. It has two surfaces and four borders, superior, inferior, anterior and posterior. Both surfaces are marked by grooves for nerves and vessels. The tick superior border bears alae separated by deep groove. The inferior border articulates with median nasal crests of the maxillae and the palatine bones. The anterior border is the longest and articulates in its upper half with the perpendicular plate of the ethmoid bone. The posterior border is concave, separating the posterior nasal apertures. ZYGOMATIC BONE Each zygomatic bone forms the prominence of a cheek, contributes to the floor and lateral wall of the orbit and the walls of the temporal and infratemporal fossae, and completes the zygomatic arch. It is described as having three surfaces, five borders and two processes. The surfaces are lateral, posteromedial and orbital. The lateral (facial) surface is convex. Its upper part bears zygomaticofacial foramen for the zygomaticofacial nerve and vessels. The posteromedial (temporal) surface articulates anteriorly with zygomatic process of the maxilla, and greater posterior smooth part extends up posteriorly on its frontal process forming anterior wall of temporal fossa. This surface bears the zygomaticotemporal foramen. The orbital surface is smooth and concave and forms anterolateral ppart of the orbital floor and adjacent lateral wall. It bears zygomatico-orbital foramen which leads into the zygomatic canal. The concave anterosuperior (orbital) border forms inferolateral part of the orbital opening. The anteroinferior (maxillary) border articulates with the maxilla. The posterosuperior (temporal) is convex above and concave below. The posteroinferior border serves as attachment of masseter. The posteromedial border articulates with the greater wing of the sphenoidal bone above and maxilla below. The frontal process articulates above with the zygomatic process of the frontal bone and behind with greater wing of the sphenoidal bone.  The temporal process, directed backwards, articulates with zygomatic process of the temporal bone to complete the zygomatic arch. PALATINE BONE The palatine bone is paired bone, posteriorly placed in the nasal cavity between the maxilla and the pterygoid process of the sphenoidal bone. It contributes to the floor and lateral wall of the nose, to the floor of the orbit, to the pterygopalanine and pterygoid fossae. It is irregular in shape with two plates, horizontal and perpendicular, arranged as an L- shape, and three processes, pyramidal, orbital and sphenoidal. Horizontal plate The horizontal plate is guadrilateral, with two surfaces, nasal and palatine, and four borders, anterior, posterior, lateral and medial. The nasal, superior surface is concave, and forms the posterior part of the nasal floor. The palatine, inferior surface, with its fellow, forms the posterior quarter of the bony palate. The posterior border is thin and concave. Medially, with its fellow from the opposite side, the posterior border forms a median posterior nasal spine. The anterior border articulates with the palatine process of the maxilla. The lateral border is continuous with the perpendicular plate of the palatine bone. The medial border articulates with its fellow in the midline and forms posterior part of the nasal crest which articulates with the posterior part of the lower edge of the vomer. Perpendicular plate The perpendicular plate is thin and has two surfaces, nasal and maxillary, and four borders, anterior, posterior, superior and inferior. The nasal, medial surface bears two crests, conchal and ethmoidal. Inferiorly, the nasal surface is concave where it contributes to part of the inferior nasal meatus. Above this is horizontal crest that articulates with inferior nasal concha. Above the conchal crest there is shallow depression which forms a part of the middle nasal meatus. This depression is limited above by an ethmoidal crest for the middle nasal concha, above which a narrow, horizontal groove forms part of the superior nasal meatus. The maxillary, lateral surface is largely rough and irregular and articulates with nasal surface of the maxilla. Posterosuperiorly it forms a smooth medial wall to the pterygopalatine fossa. Its anterior area, also smooth, overlaps the maxillary hiatus from behind to form a posterior part of the medial wall of the maxillary sinus. Posteriorly on the maxillary surface there is deep descending greater palatine groove. This groove is converted into the canal by the maxilla. The greater palatine canal transmits the greater palatine vessels and nerv. The anterior border is thin and irregular. Level with the conchal crest, a pointed lamina projects below and behind the maxillary process of the inferior concha and articulates with it and so appears in the medial wall of the maxillary sinus. The posterior border articulates with medial pterygoid plate.  Orbital and sphenoidal processes project from the superior border, and are separated by the sphenopalatine notch (converted into a foramen by articulation with the body of the sphenoid). The inferior border is continuous with the lateral border of the horizontal plate. Pyramidal process The pyramidal process slopes down posterolaterally from the junction of the horizontal and perpendicular palatine plates into the angle between the pterygoid plates of the sphenoid bone. On its posterior surface there is a smooth, grooved triangular area which completes, with pterygoid plates, the pterygoid fossa. Orbital process The orbital process is directed superolaterally from the anterosuperior angle of the perpendicular plate. It has three articular and two non-articular surfaces. It articulates with maxilla, sphenoidal and ethmoidal bones. Of the non-articular, the superior orbital forms small posterior part of the orbital floor. The lateral surface forms part of the anterior wall of the ptreygopalatine fossa. Sphenoidal process The sphenoidal process is a thin plate that is directed superomedially from the superoposterior angle of the perpendicular plate. Its superior surface articulates with sphanoidal bone (body and root of the medial pterygoid plate). The lateral surface with its anterior smooth pars forms part of the medial wall of the pterygoid fossa. The inferomedial surface forms part of root and lateral wall of the nose. HYOID BONE The hyoid bone is a small bone that has the shape of the horseshoe, or the letter U. It is placed in the anterior side of the neck, between the mandible and the larynx. Main parts of the hyoid bone are the body and two paired processes, the greater and the lesser horns. The body has two surfaces, anterior and posterior and two borders, superior and inferior. The greater horns project posteriorly and superiorly from the body and the lesser horns start superiorly from the place where greater horns joins the body. The hyoid bone connects the floor of the oral cavity in front with the pharynx behind and the larynx bellow.