Download The frontal bone:-

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.
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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.
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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.
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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.
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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.
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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.
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Fig.12: the inferior conchae
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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.
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Fig.13: the palatine bone
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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.
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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
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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.
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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.
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A
B
Fig. 16: Fetal skull
A: anterior view
B: lateral view
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