Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
The facial bones The maxilla:The right and left maxillae are the principal bones of the facial skeleton. Each maxilla takes part in the formation of the orbital floor, the lateral wall of the nasal cavity and the greater anterior part of the hard palate. The two bones meet in the midline at the intermaxillary suture and form the lower margin of the nasal aperture. The parts of maxilla are: 1) The body 2) The frontal processes 3) The zygomatic processes 4) The alveolar processes 5) The palatine processes The body of the bone contains a large pyramid-shaped cavity lined with mucous membrane called the maxillary air sinus. The maxillary surface are:1. The anterior surface of the body formed the facial skeleton below the infraorbital margin. A little below the middle of this margin is the infra-orbital foramen through which the infraorbital nerve and artery reach face. The medial edge of the anterior surface formed the lateral and inferior boundary of the anterior nasal cavity. 2. The orbital surface forms most of the medial part of the floor of the orbit. Posteriorly on this surface is the infra-orbital groove, through which anteriorly becomes continuous with the canal of that name. This surface articulate laterally with the zygomatic bone and medially with the orbital plate of the ethmoid bone and the lacrimal bone. 3. The infratemporal surface formed the anterior wall of the pterygopalatine fossa medially and the infratemporal fossa laterally. On the upper part of this surface there are one or more foramina for the posterior superior vessels and nerves to maxillary tubercle. 4. The posterior surface which is convex surface that contains foramen for transmits superior alveolar nerve and blood vessel. The pterygomaxillary fissure is located on the medial wall of the infratemporal fossa and formed by the interval between the pterygoid processes of the sphenoid bone and the posterior aspect of the maxilla, which transmits the maxillary vessels. 5. The nasal surface of the maxilla forms the anterior part of the lateral wall of the nasal cavity and has a rough a rough area behind for articulation with the perpendicular plate of the palatine bone. On this rough surface there is a smooth, obliquely running groove, which in the articulated skull is converted into a canal (the greater palatine canal) by a corresponding groove on the palatine bone. Through this canal the greater palatine vessels and nerve reach the palate. I In front of the arc for the palatine bone there is a large opening, which leads into the maxillary sinus. Above the opining the ethmoidal bulla and uncinate process encroach on the upper part of the opening. Further forwards is the groove for the nasolacrimal duct. The anterior boundary of the groove is continuous below with the conchal crest for the anterior part of the inferior conchae. Medially the nasolacrimal groove is closed in by processes of the lacrimal bone and the inferior conchae. The frontal process is a thin flattened projection, which extends upwards and articulates with the frontal bone. This process articulates laterally with the nasal bone, and medially with the lacrimal and ethmoidal bones. The lateral edge forms the medial margin of the orbital cavity. The posterior part of this process is hollowed out and this together with the hollow on the lacrimal bone forms the lacrimal groove. The medial surface forms the upper anterior part of the lateral wall of the nasal cavity. The zygomatic process projects laterally from the upper lateral part of the body and articulates with the zygomatic bone. It is thickened in relation to the force transmitted to it when the teeth are clenched. The inferior most aspects of the two maxillae, which is called the alveolar process, which are thick house the 16 maxillary teeth, forming the upper dental arch. Each maxilla contains a central, lateral and canine, whose single root forms a prominent tuberosity on the maxilla, known as canine eminence. Medial to the canine eminence is a fossa superior to the two incisors called the incisive fossa, and a similar fossa located lateral to the canine eminence called as canine fossa. The maxillary dental arch also contains the sockets for the roots of the two premolars and three molars. The palatal process projects medially at the junction of the body with the alveolar process and articulate by a suture with the corresponding palatal process of the opposite side. These processes form the greater part of the hard palate and their posterior margins articulate with the horizontal processes of the palatine bone. Above, the median crest formed by the fusion of the two palatal processes of the maxillae articulates behind with the vomer and in front with the septal cartilage. The incisive fossa is a small triangular depression in the hard palate behind the central incisor teeth. The fossa leads upwards into a canal in each palatine process. II Fig. 7: maxilla anterior aspect The zygomatic bone:This formed the prominence of the cheek on each side. The bone has a lateral subcutaneous surface, a posterior surface in the temporal fossa and a medial surface in the orbit. The anterior curved margin of the bone formed the lateral and inferior margins of the orbital cavity. From the orbital margin a process passes backwards and articulates with the greater wing of sphenoid bone, thus forming the anterior part of the lateral wall and adjacent part of the floor of the orbital cavity. The zygomatic bone formed the anterior boundary of the inferior orbital fissure. On the orbital surface there are two zygomatico-orbital foramina, which are continuous with the zygomaticofacial and zygomatico temporal canals for the nerves of this name; the foramen for the zygomaticofacial nerve is on the lateral surface of the bone. The anteriorinferior part articulate with the maxilla and on the posterior surface is the foramen for the zygomaticotemporal nerve. The bone is prolonged backwards as the temporal process, which articulates with the zygomatic process of the temporal bone formed the zygomatic arch, as the frontal process, which articulates with the zygomatic process of the frontal bone. III Fig.8: zygomatic bone The lacrimal bone:This is a thin scale of bone, which forms the medial wall of the lacrimal groove and the medial wall of the upper part of the nasolacrimal canal. The lower part of the bone is in the lateral wall of the middle meatus of the nose. The lacrimal bone articulate below with the lacrimal process of the inferior conchae, in front with the maxilla, above with the frontal bone, and behind with the ethmoid bone. IV Fig.9: lacrimal bone The nasal bone:The two nasal bones formed the bridge of the nose and articulate with each other in the midline. Superiorly each bone articulates with the frontal bone and laterally with frontal process of the maxilla. The cartilage of the external nose is attached to its inferior border. In the midline the two bones project backwards and formed part of the septum of the nose. On the inner surface of each bone there is a longitudinal groove in which run the anterior ethmoidal vessels and nerve. They pass on to the external surface of the nose between the bone and cartilage as the external nasal vessels and nerve. Fig.10: nasal bone The vomer bone:This is median bone, which forms the postero-inferior part of the nasal septum. Posteriorly its upper margin is flattened to form two alae, which articulate with the inferior surface of the body of the sphenoid bone. Its smooth posterior margin forms the free edge of the septum. Inferiorly it articulates with the bones of the hard palate and antero-superiorly with the perpendicular plate of the ethmoid bone and the septal cartilage. V Fig.11: the vomer bone The inferior nasal conchae:This consists of a thin plate of bone on the lower part of the lateral wall of the nasal cavity from which it projects medially and then downwards enclosing the inferior meatus. Its upper lateral edge is attached, in front, to a ridge on the maxilla and behind to a ridge on the palatine bone. The middle part of the bone has three processes: 1st process passing upwards, which close in the lower part of the nasolacrimal duct 2nd process, which articulates with the ethmoid bone. 3rd process, between these two, downwards and articulates with the maxilla. All these processes reduce the size of the opening of the maxillary sinus. VI Fig.12: the inferior conchae VII The palatine bone:The palatine bone has 1. a perpendicular plate 2. a horizontal plate The perpendicular plate terminates superiorly in the orbital process laterally and sphenoidal process medially, separated by a notch, which with the body f the sphenoid bone, forms the sphenopalatine foramen. Through this foramen pass vessels and nerves into the nasal cavity. . The orbital process formed the most posterior part of the floor of the orbital cavity and articulates with the maxilla anteriorly and the sphenoid bone and the labyrinth of the ethmoid bone medially. The sphenoidal process is directed medially and articulates with the inferior surface of the body of the sphenoid bone anterior to the root of the medial pterygoid plate. The lateral surface of the perpendicular plat in front articulates with the medial surface of the maxilla, but behind it forms the medial wall of the pterygopalatine fossa. The medial surface formed part of the lateral wall of the nasal cavity. On this surface there is a horizontal ridge for articulation with the inferior conchae. The posterior border terminating inferiorly in the thickened pyramidal process, articulate in its upper part with the pterygoid process. Inferiorly, where the pterygoid plates separate, this process occupies the interval between them. The horizontal plates of the two palatine bones formed the posterior part of the hard palate, and articulate in front with the palatal processes of the maxillae. The free posterior margin of the horizontal plate is smooth and forms the posterior edge of the hard palate. The crest formed in the midline by the union of the horizontal plates of the right and left bones articulates with the vomer. At the lateral angle of the horizontal process inferiorly are the openings of the greater and lesser palatine foramen, which lead to the canals. The lesser palatine canals pass upwards in the tubercle of the palatine bone and join the greater palatine canal formed by the articulation of the perpendicular plate with the maxilla in the lateral wall of the nose. VIII Fig.13: the palatine bone IX The mandible:The mandible consists of a horseshoe-shaped body and a pair of rami. The body consisting of two lateral parts which are united anteriorly in the midline where a vertical ridge, the symphysis menti, indicates the site of the fusion. The ridge of the symphysis menti terminated below in the mental protuberance. The ramus is projecting upwards from the body posteriorly on each side, which is flattened vertical plate of bone. The posterior margin of the ramus meets the lower border of the body at the angle. Above each ramus had two projections, the coronoid process in front and the condyloid process behind; the processes are separated by the mandibular notch. The condyloid process had a head with an articular surface above and a lower narrower portion, the neck. The head articulates with the squamous part of the temporal bone at the tempromandibular joint. The upper border of the mandible is the alveolar margin, and in adult it contains 16 sockets for the roots of the teeth. The inferior margin is a thickened bar of bone, which greatly strengthens the body, which is called the base. On the outer aspect of the body, midway between the superior and inferior borders opposite the 2nd premolar tooth, is the mental foramen for the mental nerve and vessels. Its opining is directed backwards. The oblique line passes upwards and backwards from the mental foramen and becomes continuous with the anterior margin of the ramus. The digastric fossa is a small roughened depression on the base, on the either side of the symphysis menti. The inner aspect of the body had in the median plane are seen the mental spines. An oblique ridge, the mylohyoid ridge, which passes downwards and forwards from behind the last molar tooth. They line becomes indistinct in front where it terminates close to the mental spines above anterior part of the mylohyoid a depression for the sublingual fossa for the sublingual gland and below the ridge posteriorly a depression for the submandibular fossa for the submandibular gland. Two small tubercles lie close to the midline. The medial surface of the mandible above the mylohyoid ridge is related to structure in the floor of the mouth, especially the sublingual gland in front. The lingual nerve lies on the bone just above the posterior end of the mylohyoid ridge. The surface below the ridge is related to structures in the upper part of the neck. The submandibular gland lies in a shallow fossa below the posterior half of the ridge. At about the middle of the inner surface of the ramus, about the level of the crown of the last molar tooth, a foramen leads into the mandibular canal for the inferior alveolar nerve and artery. The sharp and prominent anterior margin of the foramen is called the lingula. Leading downwards on the medial surface of the ramus from the mandibular foramen called the mylohyoid groove in which lies the mylohyoid nerve. X The head has a convex and transversely elongated articular surface. The long axis of the head is directed obliquely so that if the axes of both sides were continued medially they would meet near the anterior margin of the foramen magnum, at an angle of 140-159. The coronoid process is directed upwards as a flattened triangular projection. Its anterior border is continuous with the sharp anterior margin of the ramus. (A) (B) Fig 14: The mandible A: medial aspect B: lateral aspect XI Age changes in the skull At birth the skull forms a much larger proportion of the fetal body length than in the adult. In the newborn the distance from the lower border of the mandible to the inferior orbital margin is about one-third of the total height of the skull. In the adult it is about one-half, due to both growth of the maxilla and mandible in which the permanent teeth erupt, and also the growth in height of the maxillary sinuses and the nasal cavity. The orbits are proportionately larger in the infant than in the later years. The skull at birth consists of a number of separate bones connected at their margins by dense membranous tissue as well as cartilaginous area, especially in the base. In parts of the skull, the amount of membranous tissue between adjacent bones is extensive and form fontanelles. Clinically the anterior and posterior fontanelles are most important and are easily examined in the midline of the vault. The anterior fontanelle is the diamond-shaped space, which is present in the midline between the frontal and parietal bones. Extension of ossification into the membrane results in the closure of the fontanelle between the ages of 18-24 months. The posterior fontanelle is a smaller triangular area bounded by the occipital and parietal bones; it is close at the end of the 1st year and can no longer be palpated. Other fontanelles are found at the junction of the greater wing of the sphenoid bone with the temporal and parietal bones, and at the meeting point of the temporal, parietal, and occipital bones. The edges of the bones are not serrated in infancy. Growth takes place at the edges so that the whole volume of the skull increases. Growth of the vault stops at the age of 16 years. At birth some bones have sutures, which usually disappear later. These include the sutures between the squamous and tympanic parts of the temporal bone and between the greater wing of the sphenoid bone and the remainder of that bone. These sutures disappear during the 1st year of life. The two halves of the frontal bone begin to unite during the 2 nd year and this is completed by the 6th year; exceptionally, a median suture persists throughout life and is called a metopic suture. After 20 years the sutures begin diaper. In old age the bones become lighter and thinner. The paranasal sinuses are absent at birth except for small depression in the wall of the nasal cavity, which represent the beginnings of the maxillary and sphenoidal sinuses. With the enlargement of the facial skeleton the nasal cavity becomes relatively larger from above downwards and the orbits become more widely separated from the mouth. At the same time the hard palate sinks to a lower level relative to the posterior part of the skull. With the growth of the face there is a gradual forwards extension of the vomer at the expense of the septal cartilage. XII Extensive changes occur in the mandible from birth until old age. The two halves of the mandible are connected at the symphysis menti by fibrous tissue until the age of one year, when bony union occurs. The mandible shows striking changes associated with the growth and eruption of the teeth. At birth the alveolar process of the mandible is larger and contains not only the crowns and roots of the primary teeth, but also the rudiments of the permanent teeth. The part of the mandible below the alveolar process is poorly developed so that the mental foramen is relatively close to the lower margin of the bone. During the eruption of the teeth the body of the mandible elongates and there is a simultaneous absorption and addition of bone on the anterior and posterior borders of the ramus respectively. At birth the ramus of the mandible projects only a little above the level of the alveolar margin and the angle is very obtuse (175°); in old age this angle becomes less obtuse (140°) owing to the absorption of the alveolar margin after the teeth have been shed or extracted. Variation in the shape of the skull in the gender The male skull is generally larger and heavier than female. The muscular impressions are more marked and the mastoid processes and the superciliary ridge are larger. The female skull has a capacity about one-tenth less than that of the male of the same race. The facial skeleton is smaller in proportion and the jaws are narrower and less prominent. This difference is very difficult to determine with certainty the sex of an individual by means of the skull. XIII A B Fig. 16: Fetal skull A: anterior view B: lateral view XIV