1.Temporal bone
2.maxilla. palatine bone
3.nasal, lacrimal, zygomatic bone, inferior nasal concha,
vomer, mandible, hyoid bone
Lesson # 3
Theme 1. Temporal bone.
The Temporal
Bone (Os Temporale) is
situated at the sides and base of the skull. Each consists of the squama, the petrous (pyramid) with mastoid process and
tympanic part. The squama has a groove for the middle
temporal artery and the temporal line. It is a long the zygomatic
process. The mandibular fossa is bounded, in front, by the articular tubercle.
Pars petrosa [pyramis] has a base and apex, and anterior, posterior and
inferior surfaces, and three angles, and contains the of
the organ of hearing and balance. The base is fused with the internal
surfaces of the squama and mastoid portion. The
anterior surface has eminentia arcuata,
the tegmen tympani; hiatus and sulcus canalis nervi
petrosi majoris; laterally
hiatus and sulcus canalis nervi
petrosi minoris; near the
apex of the bone, the termination of the carotid canal (foramen internus); above this canal the trigeminal impression. The
posterior surface has the internal acoustic meatus, the aperture externa aqueductus vestibuli, the subarcuate
fossa. The inferior surface contain foramen coroticum externus, the jugular
fossa, a small opening of the aqueductus cochleae,
the styloid process and the stylomastoid
foramen. Mastoid Process is perforated by the mastoid foramen and carries the
sigmoid sinus sulcus. A section of the mastoid process shows it to be hollowed
out into a number of spaces, the mastoid cells and mastoid antrum.
Tympanic Part (pars tympanica)
forms the walls and the floor of the bony external acoustic meatus. It borders
the tympanomastoid fissure.
Canals of the temporal bone:
1. Carotid canal
starts in external foramen on lower surface of the piramis
and finishes by internal opening in apex of the piramis.
2. Facial canal starts
in internal acoustic meatus on back surface of the piramis
and finishes in stylomastoid foramen on lower surface
of the piramis.
3. Musculotubarius canal is divided
into semicanalis m. tensoris
tympani and semicanalis tubae
auditivae. It starts on anterior margin of the piramis and leads to the tympanic cavity.
4. Caroticotympanic canaliculi
(paired) start on medial wall of the external carotid foramen and lead to the the tympanic cavity.
5. Canaliculus for chorda tympani
starts in facial canal, passes through the tympanic cavity and finishes in petrotympanic fissura.
6. Tympanic canaliculus
starts in the petrosal fossula
and finishes in hiatus canalis nervi petrosi minoris.
7. Mastoid canaliculus
on the floor of the jugular fossa and passes to the tympanomastoid
fissura.
The temporal bones are situated at the sides and base of the skull. Each
consists of five parts, viz., the squama,
the petrous, mastoid, and tympanic parts, and the styloid process.
The Squama (squama
temporalis).—The squama forms the anterior and upper part of the bone, and
is scale-like, thin, and translucent.
Surfaces.—Its outer
surface is smooth and convex; it affords attachment to the Temporalis
muscle, and forms part of the temporal fossa; on its hinder part is a vertical
groove for the middle temporal artery. A curved line, the temporal line,
or supramastoid crest, runs backward
and upward across its posterior part; it serves for the attachment of the
temporal fascia, and limits the origin of the Temporalis muscle. The boundary
between the squama and the mastoid portion of the
bone, as indicated by traces of the original suture, lies about
Left temporal bone. Inner surface.
The anterior root, continuous with the lower border, is short but broad
and strong; it is directed medialward and ends in a
rounded eminence, the articular tubercle (eminentia
articularis). This tubercle forms the front
boundary of the mandibular fossa, and in the fresh state is covered with
cartilage. In front of the articular tubercle is a small triangular area which
assists in forming the infratemporal fossa; this area
is separated from the outer surface of the squama by
a ridge which is continuous behind with the anterior root of the zygomatic process, and in front, in the articulated skull,
with the infratemporal crest on the great wing of the
sphenoid. Between the posterior wall of the external acoustic meatus and the
posterior root of the zygomatic process is the area
called the suprameatal triangle (Macewen), or mastoid fossa, through which an
instrument may be pushed into the tympanic antrum. At
the junction of the anterior root with the zygomatic
process is a projection for the attachment of the temporomandibular
ligament; and behind the anterior root is an oval depression, forming part of
the mandibular fossa, for the reception of the condyle of the mandible. The mandibular
fossa (glenoid fossa) is bounded,
in front, by the articular tubercle; behind, by the tympanic part of the bone,
which separates it from the external acoustic meatus; it is divided into two
parts by a narrow slit, the petrotympanic
fissure (Glaserian fissure). The
anterior part, formed by the squama, is smooth,
covered in the fresh state with cartilage, and articulates with the condyle of
the mandible. Behind this part of the fossa is a small conical eminence; this
is the representative of a prominent tubercle which, in some mammals, descends
behind the condyle of the mandible, and prevents its backward displacement. The
posterior part of the mandibular fossa, formed by the tympanic part of the
bone, is non-articular, and sometimes lodges a portion of the parotid gland.
The petrotympanic fissure leads into the middle ear
or tympanic cavity; it lodges the anterior process of the malleus, and
transmits the tympanic branch of the internal maxillary artery. The chorda
tympani nerve passes through a canal (
The internal surface of the squama
is concave; it presents depressions corresponding to the convolutions of the
temporal lobe of the brain, and grooves for the branches of the middle
meningeal vessels.
Borders.—The superior border is
thin, and bevelled at the expense of the internal table, so as to overlap the
squamous border of the parietal bone, forming with it the squamosal suture.
Posteriorly, the superior border forms an angle, the parietal notch,
with the mastoid portion of the bone. The antero-inferior
border is thick, serrated, and bevelled at the expense of the inner table
above and of the outer below, for articulation with the great wing of the
sphenoid.
Mastoid Portion (pars mastoidea).—The mastoid portion forms the posterior part of the bone.
Coronal section of right temporal bone.
Surfaces.—Its outer surface is rough,
and gives attachment to the Occipitalis and Auricularis posterior. It is perforated by numerous
foramina; one of these, of large size, situated near the posterior border, is
termed the mastoid foramen; it transmits a vein to the transverse sinus
and a small branch of the occipital artery to the dura
mater. The position and size of this foramen are very variable; it is not
always present; sometimes it is situated in the occipital bone, or in the
suture between the temporal and the occipital. The mastoid portion is continued
below into a conical projection, the mastoid process, the size and form
of which very somewhat; it is larger in the male than in the female. This
process serves for the attachment of the Sternocleidomastoideus,
Splenius capitis, and Longissimus
capitis. On the medial side of the process is a deep
groove, the mastoid notch (digastric fossa), for the attachment
of the Digastricus; medial to this is a shallow
furrow, the occipital groove, which lodges the occipital artery.
The inner surface of the mastoid portion presents a
deep, curved groove, the sigmoid sulcus, which lodges part of the
transverse sinus; in it may be seen the opening of the mastoid foramen. The
groove for the transverse sinus is separated from the innermost of the mastoid
air cells by a very thin lamina of bone, and even this may be partly deficient.
Borders.—The superior
border of the mastoid portion is broad and serrated, for articulation with
the mastoid angle of the parietal. The posterior border, also serrated,
articulates with the inferior border of the occipital between the lateral angle
and jugular process. Anteriorly the mastoid portion is fused with the
descending process of the squama above; below it
enters into the formation of the external acoustic meatus and the tympanic
cavity.
A section of the mastoid process shows it to be hollowed out
into a number of spaces, the mastoid cells, which exhibit the greatest
possible variety as to their size and number. At the upper and front part of
the process they are large and irregular and contain air, but toward the lower
part they diminish in size, while those at the apex of the process are
frequently quite small and contain marrow; occasionally they are entirely absent,
and the mastoid is then solid throughout. In addition to these a large
irregular cavity is situated at the upper and front part of the bone. It is
called the tympanic antrum, and must be
distinguished from the mastoid cells, though it communicates with them. Like
the mastoid cells it is filled with air and lined by a prolongation of the
mucous membrane of the tympanic cavity, with which it communicates. The
tympanic antrum is bounded above by a thin plate of
bone, the tegmen tympani, which
separates it from the middle fossa of the base of the skull; below by the
mastoid process; laterally by the squama just below
the temporal line, and medially by the lateral semicircular
canal of the internal ear which projects into its cavity. It opens in front
into that portion of the tympanic cavity which is known as the attic or epitympanic recess. The tympanic antrum is a cavity of some considerable size at the time of
birth; the mastoid air cells may be regarded as diverticula from the antrum, and begin to appear at or before birth; by the
fifth year they are well-marked, but their development is not completed until
toward puberty.
Petrous Portion (pars petrosa [pyramis]).—The
petrous portion or pyramid is pyramidal and is wedged in at the base of
the skull between the sphenoid and occipital. Directed medialward,
forward, and a little upward, it presents for examination a base, an apex,
three surfaces, and three angles, and contains, in its interior, the essential
parts of the organ of hearing.
Base.—The base is fused with the internal surfaces of the squama and mastoid portion.
Apex.—The apex, rough and uneven, is received into the
angular interval between the posterior border of the great wing of the sphenoid
and the basilar part of the occipital; it presents the anterior or internal
orifice of the carotid canal, and forms the postero-lateral
boundary of the foramen lacerum.
Surfaces.—The anterior surface forms the posterior
part of the middle fossa of the base of the skull, and is continuous with the
inner surface of the squamous portion, to which it is united by the petrosquamous suture, remains of which are
distinct even at a late period of life. It is marked by depressions for the
convolutions of the brain, and presents six points for examination: (1) near
the center, an eminence (eminentia
arcuata) which indicates the situation of the
superior semicircular canal; (2) in front of and a
little lateral to this eminence, a depression indicating the position of the
tympanic cavity: here the layer of bone which separates the tympanic from the
cranial cavity is extremely thin, and is known as the tegmen
tympani; (3) a shallow groove, sometimes double, leading lateralward and backward to an oblique opening, the hiatus
of the facial canal, for the passage of the greater superficial petrosal nerve and the petrosal
branch of the middle meningeal artery; (4) lateral to the hiatus, a smaller
opening, occasionally seen, for the passage of the lesser superficial petrosal nerve; (5) near the apex of the bone, the
termination of the carotid canal, the wall of which in this situation is
deficient in front; (6) above this canal the shallow trigeminal impression
for the reception of the semilunar ganglion.
The posterior surface forms the front part of the
posterior fossa of the base of the skull, and is continuous with the inner
surface of the mastoid portion. Near the center is a
large orifice, the internal acoustic meatus, the size of which varies
considerably; its margins are smooth and rounded, and it leads into a short
canal, about
Diagrammatic view of the fundus of the right internal acoustic meatus:
1. Crista falciformis. 2. Area facialis, with (
The inferior surface is rough and irregular, and
forms part of the exterior of the base of the skull. It presents eleven points
for examination: (1) near the apex is a rough surface, quadrilateral in form,
which serves partly for the attachment of the Levator
veli palatini and the
cartilaginous portion of the auditory tube, and partly for connection with the
basilar part of the occipital bone through the intervention of some dense
fibrous tissue; (2) behind this is the large circular aperture of the carotid
canal, which ascends at first vertically, and then, making a bend, runs
horizontally forward and medialward; it transmits
into the cranium the internal carotid artery, and the carotid plexus of nerves;
(3) medial to the opening for the carotid canal and close to its posterior
border, in front of the jugular fossa, is a triangular depression; at the apex
of this is a small opening, the aquaeductus
cochleae, which lodges a tubular prolongation of the dura
mater establishing a communication between the perilymphatic
space and the subarachnoid space, and transmits a vein from the cochlea to join
the internal jugular; (4) behind these openings is a deep depression, the jugular
fossa, of variable depth and size in different skulls; it lodges the bulb
of the internal jugular vein; (5) in the bony ridge dividing the carotid canal
from the jugular fossa is the small inferior tympanic canaliculus
for the passage of the tympanic branch of the glossopharyngeal nerve; (6) in
the lateral part of the jugular fossa is the mastoid canaliculus
for the entrance of the auricular branch of the vagus
nerve; (7) behind the jugular fossa is a quadrilateral area, the jugular
surface, covered with cartilage in the fresh state, and articulating with
the jugular process of the occipital bone; (8) extending backward from the
carotid canal is the vaginal process, a sheath-like plate of bone, which
divides behind into two laminae; the lateral lamina
is continuous with the tympanic part of the bone, the medial with the lateral
margin of the jugular surface; (9) between these laminae
is the styloid process, a sharp spine,
about
Left temporal bone. Inferior surface.
Angles.—The superior angle, the
longest, is grooved for the superior petrosal sinus,
and gives attachment to the tentorium cerebelli; at
its medial extremity is a notch, in which the trigeminal nerve lies. The posterior
angle is intermediate in length between the superior and the anterior. Its
medial half is marked by a sulcus, which forms, with a corresponding sulcus on
the occipital bone, the channel for the inferior petrosal
sinus. Its lateral half presents an excavation—the jugular fossa—which,
with the jugular notch on the occipital, forms the jugular foramen; an
eminence occasionally projects from the center of the
fossa, and divides the foramen into two. The anterior angle is divided
into two parts—a lateral joined to the squama by a
suture (petrosquamous), the remains of which
are more or less distinct; a medial, free, which articulates with the spinous process of the sphenoid.
At the angle of junction of the petrous part and the squama are two canals, one above the other, and separated
by a thin plate of bone, the septum canalis musculotubarii (processus
cochleariformis); both canals lead into the
tympanic cavity. The upper one (semicanalis
m. tensoris tympani) transmits the Tensor
tympani, the lower one (semicanalis tubae auditivae) forms the
bony part of the auditory tube.
The tympanic cavity, auditory ossicles,
and internal ear, are described with the organ of hearing.
Tympanic Part (pars tympanica).—The tympanic part is a curved plate of bone lying below the squama and in front of the mastoid process.
Surfaces.—Its postero-superior
surface is concave, and forms the anterior wall, the floor, and part of the
posterior wall of the bony external acoustic meatus. Medially, it presents a
narrow furrow, the tympanic sulcus, for the attachment of the tympanic membrane.
Its antero-inferior surface is
quadrilateral and slightly concave; it constitutes the posterior boundary of
the mandibular fossa, and is in contact with the retromandibular
part of the parotid gland.
Borders.—Its lateral border is free
and rough, and gives attachment to the cartilaginous part of the external
acoustic meatus. Internally, the tympanic part is fused with the petrous
portion, and appears in the retreating angle between it and the squama, where it lies below and lateral to the orifice of
the auditory tube. Posteriorly, it blends with the squama
and mastoid part, and forms the anterior boundary of the tympanomastoid
fissure. Its upper border fuses laterally with the back of the postglenoid process, while medially it bounds the petrotympanic fissure. The medial part of the lower
border is thin and sharp; its lateral part splits to enclose the root of
the styloid process, and is therefore named the vaginal
process. The central portion of the tympanic part is thin, and in a
considerable percentage of skulls is perforated by a hole, the foramen of Huschke.
The external acoustic meatus is nearly
Styloid Procéss (processus
styloideus).—The
styloid process is slender, pointed, and of varying
length; it projects downward and forward, from the under surface of the
temporal bone. Its proximal part (tympanohyal)
is ensheathed by the vaginal process of the tympanic
portion, while its distal part (stylohyal)
gives attachment to the stylohyoid and stylomandibular ligaments, and to the Styloglossus,
Stylohyoideus, and Stylopharyngeus
muscles. The stylohyoid ligament extends from the
apex of the process to the lesser cornu of the hyoid
bone, and in some instances is partially, in others completely, ossified.
Structure.—The structure of the squama is like that of the other cranial bones: the mastoid
portion is spongy, and the petrous portion dense and hard.
The three principal parts of the tempora bone
at birth. 1. Outer surface of petromastoid part. 2.
Outer surface of tympanic ring. 3. Inner surface of squama.
Temporal bone at birth. Outer aspect.
Ossification.—The temporal bone is
ossified from eight centers, exclusive of
those for the internal ear and the tympanic ossicles,
viz., one for the squama including the zygomatic process, one for the tympanic part, four for the
petrous and mastoid parts, and two for the styloid
process. Just before the close of fetal life the
temporal bone consists of three principal parts: 1. The squama
is ossified in membrane from a single nucleus, which appears near the root of
the zygomatic process about the second month. 2. The petromastoid part is developed from four centers, which make their appearance in the cartilaginous
ear capsule about the fifth or sixth month. One (prootic)
appears in the neighborhood of the eminentia arcuata, spreads in
front and above the internal acoustic meatus and extends to the apex of the
bone; it forms part of the cochlea, vestibule, superior semicircular
canal, and medial wall of the tympanic cavity. A second (opisthotic)
appears at the promontory on the medial wall of the tympanic cavity and
surrounds the fenestra cochleae; it forms the floor of the tympanic cavity and
vestibule, surrounds the carotid canal, invests the lateral and lower part of
the cochlea, and spreads medially below the internal acoustic meatus. A third (pterotic) roofs in the tympanic cavity and antrum; while the fourth (epiotic)
appears near the posterior semicircular canal and
extends to form the mastoid process (Vrolik). 3. The tympanic
ring is an incomplete circle, in the concavity of which is a groove, the
tympanic sulcus, for the attachment of the circumference of the tympanic
membrane. This ring expands to form the tympanic part, and is ossified in
membrane from a single center which appears about the
third month. The styloid process is
developed from the proximal part of the cartilage of the second branchial or hyoid arch by two centers:
one for the proximal part, the tympanohyal,
appears before birth; the other, comprising the rest of the process, is named
the stylohyal, and does not appear
until after birth. The tympanic ring unites with the squama
shortly before birth; the petromastoid part and squama join during the first year, and the tympanohyal portion of the styloid
process about the same time. The stylohyal does not
unite with the rest of the bone until after puberty, and in some skulls never
at all.
The chief subsequent changes in the temporal bone apart from
increase in size are: (1) The tympanic ring extends outward and backward to
form the tympanic part. This extension does not, however, take place at an
equal rate all around the circumference of the ring, but occurs most rapidly on
its anterior and posterior portions, and these outgrowths meet and blend, and
thus, for a time, there exists in the floor of the meatus a foramen, the foramen
of Huschke; this foramen is usually closed about
the fifth year, but may persist throughout life. (2) The mandibular fossa is at
first extremely shallow, and looks lateralward as
well as downward; it becomes deeper and is ultimately directed downward. Its
change in direction is accounted for as follows. The part of the squama which forms the fossa lies at first below the level
of the zygomatic process. As, however, the base of
the skull increases in width, this lower part of the squama
is directed horizontally inward to contribute to the middle fossa of the skull,
and its surfaces therefore come to look upward and downward; the attached
portion of the zygomatic process also becomes everted, and projects like a shelf at right angles to the squama. (3) The mastoid portion is at first quite flat, and
the stylomastoid foramen and rudimentary styloid process lie immediately behind the tympanic ring.
With the development of the air cells the outer part of the mastoid portion
grows downward and forward to form the mastoid process, and the styloid process and stylomastoid
foramen now come to lie on the under surface. The descent of the foramen is
necessarily accompanied by a corresponding lengthening of the facial canal. (4)
The downward and forward growth of the mastoid process also pushes forward the
tympanic part, so that the portion of it which formed the original floor of the
meatus and contained the foramen of Huschke is
ultimately found in the anterior wall. (5) The fossa subarcuata
becomes filled up and almost obliterated.
Articulations.—The temporal articulates with five
bones: occipital, parietal, sphenoid, mandible and zygomatic.
Theme 2. maxilla.
palatine bone
Bones of viscerocranium
Bones of viscerocranium
include: maxilla, zygomatic, nasal, palatine,
lacrimal bones, vomer, greater portion of the ethmoid, mandible and inferior nasal concha.
Maxilla -
paired bone, has a body and four processes: frontal, zygomatic,
alveolar and palatine. Frontal process riches the nasal part of the frontal
bone, medially it carries ethmoidal crest for middle
nasal concha. Zygomatic process joins zygomatic bone. Alveolar process carries dental alveoli for
insertion the teeth. Palatine process forms bony palatine.
There are four surfaces in maxillary body: anterior,
orbital, infraorbital and nasal. Anterior surface is
bordered by infraorbital margin where it is infraorbital foramen nasal surface one can find maxillary
hiatus that communicates middle nasal meatus with maxillary (Haymory) sinus.
The maxillae are the largest bones of the face, excepting the
mandible, and form, by their union, the whole of the upper jaw. Each assists in
forming the boundaries of three cavities, viz., the roof of the mouth, the
floor and lateral wall of the nose and the floor of the orbit; it 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—zygomatic, frontal, alveolar, and palatine.
The Body (corpus maxillae).—The
body is somewhat pyramidal in shape, and contains a large cavity, the maxillary
sinus (antrum of Highmore). It has
four surfaces—an anterior, a posterior or infratemporal,
a superior or orbital, and a medial or nasal.
Surfaces.—The anterior surface is
directed forward and lateralward. It presents at its
lower part a series of eminences corresponding to the positions of the roots of
the teeth. Just above those of the incisor teeth is a depression, the incisive
fossa, which gives origin to the Depressor alae nasi; to the alveolar border below the fossa is attached a
slip of the Orbicularis oris; above and a little
lateral to it, the Nasalis arises. Lateral to the
incisive fossa is another depression, the canine fossa; it is larger and
deeper than the incisive fossa, and is separated from it by a vertical ridge,
the canine eminence, corresponding to the socket of the canine tooth;
the canine fossa gives origin to the Caninus. Above
the fossa is the infraorbital foramen,
the end of the infraorbital canal; it transmits the infraorbital vessels and nerve. Above the foramen is the
margin of the orbit, which affords attachment to part of the Quadratus labii superioris. Medially, the anterior surface is limited by a
deep concavity, the nasal notch, the margin of which gives attachment to
the Dilatator naris posterior and ends below in a pointed process, which with
its fellow of the opposite side forms the anterior nasal spine.
The infratemporal
surface is convex, directed backward and lateralward,
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
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, especially prominent after the
growth of the wisdom tooth; it is rough on its lateral side for articulation
with the pyramidal process of the palatine bone and in some cases articulates
with the lateral pterygoid plate of the sphenoid. It
gives origin to a few fibers of the Pterygoideus internus.
Immediately above this is a smooth surface, which forms the anterior boundary
of the pterygopalatine fossa, and presents a groove,
for the maxillary nerve; this groove is directed lateralward
and slightly upward, and is continuous with the infraorbital
groove on the orbital surface.
The orbital surface is smooth and triangular, and
forms the greater part of the floor of the orbit. It is bounded medially
by an irregular margin which in front presents a notch, the lacrimal notch;
behind this notch the margin articulates with the lacrimal, the lamina papyracea of the ethmoid and the
orbital process of the palatine. It is bounded behind by a smooth
rounded edge which forms the anterior margin of the inferior orbital fissure,
and sometimes articulates at its lateral extremity with the orbital surface of
the great wing of the sphenoid.
Left maxilla. Nasal surface
It is limited in front by part of the circumference
of the orbit, which is continuous medially with the frontal process, and
laterally with the zyogmatic process. 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 begins at the middle of the posterior border,
where it is continuous with that near the upper edge of the infratemporal
surface, and, passing forward, ends in a canal, which subdivides into two
branches. One of the canals, the infraorbital
canal, opens just below the margin of the orbit; the other, which is
smaller, runs downward in the substance of the anterior wall of the maxillary
sinus, and transmits the anterior superior alveolar vessels and nerve to the
front teeth of the maxilla. From the back part of the infraorbital
canal, a second small canal is sometimes given off; it runs downward in the
lateral wall of the sinus, and conveys the middle alveolar nerve to the
premolar teeth. At the medial and forepart of the orbital surface just lateral
to the lacrimal groove, is a depression, which gives origin to the Obliquus oculi inferior.
The nasal surface presents a large, irregular opening
leading into the maxillary sinus. At the upper border of this aperture are some
broken air cells, which, in the articulated skull, are closed in by the ethmoid and lacrimal bones. 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 part of
the palatine bone; this surface is traversed by a groove, commencing near the
middle of the posterior border and running obliquely downward and forward; the
groove is converted into a canal, the pterygopalatine
canal, by the palatine bone. In front of the opening of the sinus is a deep
groove, the lacrimal groove, which is converted into the nasolacrimal
canal, by the lacrimal bone and inferior nasal concha; this canal opens into
the inferior meatus of the nose and transmits the nasolacrimal duct. More
anteriorly is an oblique ridge, the conchal
crest, for articulation with the inferior nasal concha. The shallow
concavity above this ridge forms part of the atrium of the middle meatus of the
nose, and that below it, part of the inferior meatus.
Left maxillary sinus opened from the exterior
The Maxillary Sinus or Antrum of Highmore (sinus maxillaris).—The
maxillary sinus is a large pyramidal cavity, within the body of the maxilla:
its apex, directed lateralward, is formed by
the zygomatic process; its base, directed medialward, by the lateral wall of the nose. 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, in the disarticulated bone, 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 above and in front; the sinus
communicates with the middle meatus of the nose, generally by two small
apertures left between the above-mentioned bones. In the fresh state, usually
only one small opening exists, near the upper part of the cavity; the other is
closed by mucous membrane. On the posterior wall are the alveolar
canals, transmitting the posterior superior alveolar vessels and nerves to
the molar teeth. The floor is formed by the alveolar process of the
maxilla, and, if the sinus be of an average size, is on a level with the floor
of the nose; if the sinus be large it reaches below this level.
Projecting into the floor of the antrum
are several conical processes, corresponding to the roots of the first and
second molar teeth; in some cases the floor is
perforated by the fangs of the teeth. The infraorbital
canal usually projects into the cavity as a well-marked ridge extending from
the roof to the anterior wall; additional ridges are sometimes seen in the
posterior wall of the cavity, and are caused by the alveolar canals. The size
of the cavity varies in different skulls, and even on the two sides of the same
skull.
The Zygomatic Process (processus
zygomaticus; malar process).—The zygomatic process is a rough triangular
eminence, situated at the angle of separation of the anterior, zygomatic, and orbital surfaces. In front it forms
part of the anterior surface; behind, it is concave, and forms part of
the infratemporal fossa; above, it is rough
and 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 Frontal Process (processus frontalis; nasal process).—The
frontal process is a strong plate, which projects upward, medialward,
and backward, by the side of the nose, forming part of its lateral boundary.
Its lateral surface is smooth, continuous with the anterior surface of
the body, and gives attachment to the Quadratus labii superioris, the Orbicularis
oculi, and the medial palpebral ligament. Its medial surface forms part
of the lateral wall of the nasal cavity; at its upper part is a rough, uneven
area, which articulates with the ethmoid, closing in
the anterior ethmoidal cells; below this is an
oblique ridge, the ethmoidal crest, the
posterior end of which articulates with the middle nasal concha, while the anterior
part is termed the agger nasi; the crest forms the upper limit of the atrium of
the middle meatus. 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: by the articulation of the medial margin of
the groove with the anterior border of the lacrimal a corresponding groove on
the lacrimal is brought into continuity, and together they form the lacrimal
fossa for the lodgement of the lacrimal sac. The lateral margin of the
groove is named the anterior lacrimal crest, and is continuous below
with the orbital margin; at its junction with the orbital surface is a small
tubercle, the lacrimal tubercle, which serves as a guide to the position
of the lacrimal sac.
The Alveolar Process (processus alveolaris).—The
alveolar process is the thickest and most spongy part of the bone. It is
broader behind than in front, and excavated into deep cavities for the
reception of the teeth. These cavities 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 septa; those for the incisors are single, but deep and narrow. The Buccinator arises from the outer surface of this process,
as far forward as the first molar tooth. When the maxillae are articulated with
each other, their alveolar processes together form the alveolar arch;
the center of the anterior margin of this arch is
named the alveolar point.
The Palatine Process (processus palatinus; palatal process).—The palatine process, thick and strong, is horizontal and projects medialward from the nasal surface of the bone. It forms a
considerable part of the floor of the nose and the roof of the mouth and is
much thicker in front than behind. Its inferior surface is concave,
rough and uneven, and forms, with the palatine process of the opposite bone, the
anterior three-fourths of the hard plate. It is perforated by numerous foramina
for the passage of the nutrient vessels; is channelled at the back part of its
lateral border by a groove, sometimes a canal, for the transmission of the
descending palatine vessels and the anterior palatine nerve from the spheno-palatine ganglion; and presents little depressions
for the lodgement of the palatine glands. When the two maxillae are
articulated, a funnel-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 or foramina of Stenson; through
each of them passes the terminal branch of the descending palatine artery and
the nasopalatine nerve. Occasionally two additional
canals are present in the middle line; they are termed the foramina of Scarpa, and when present transmit the nasopalatine nerves, the left passing through the anterior,
and the right through the posterior canal. On the under surface of the palatine
process, a delicate linear suture, well seen in young skulls, may sometimes be
noticed extending lateralward and forward 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 upper 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 incorporated with the rest of the bone. 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 part
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 bony palate and alveolar arch
Ossification.—The maxilla is ossified in membrane. Mall 40 and Fawcett 41 maintain that it is ossified from two centers
only, one for the maxilla proper and one for the premaxilla.
These centers appear during the sixth week of fetal life and unite in the beginning of the third month,
but the suture between the two portions persists on the palate until nearly
middle life. Mall states that the frontal process is developed from both centers. The maxillary sinus appears as a shallow groove on
the nasal surface of the bone about the fourth month of fetal
life, but does not reach its full size until after the second dentition. The
maxilla was formerly described as ossifying from six centers,
viz., one, the orbitonasal, forms that
portion of the body of the bone which lies medial to the infraorbital
canal, including the medial part of the floor of the orbit and the lateral wall
of the nasal cavity; a second, the zygomatic,
gives origin to the portion which lies lateral to the infraorbital
canal, including the zygomatic process; from a third,
the palatine, is developed the palatine process posterior to the
incisive canal together with the adjoining part of the nasal wall; a fourth,
the premaxillary, forms the incisive
bone which carries the incisor teeth and corresponds to the premaxilla
of the lower vertebrates; 42 a fifth, the nasal, gives rise to the frontal process and the
portion above the canine tooth; and a sixth, the infravomerine,
lies between the palatine and premaxillary centers and beneath the vomer;
this center, together with the corresponding center of the opposite bone, separates the incisive canals
from each other.
Anterior surface of maxilla at birth
Inferior surface of maxilla at birth
Articulations.—The maxilla
articulates with nine bones: two of the cranium, the frontal and ethmoid, and seven of the face, viz., the nasal, zygomatic, lacrimal, inferior nasal concha, palatine, vomer, and its fellow of the opposite side. Sometimes it
articulates with the orbital surface, and sometimes with the lateral pterygoid plate of the sphenoid.
Changes Produced in the Maxilla by Age At birth the
transverse and antero-posterior 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, owing to the development of the alveolar
process and the increase in size 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.
Palatine bone (paired)
forms part of nasal cavity, mouth, orbit and pterygopalatine
fossa. It has perpendicular and horizontal laminae.
The palatine bone is situated at the back part of the nasal
cavity between the maxilla and the pterygoid process
of the sphenoid. It contributes to the walls of three cavities: the floor and
lateral wall of the nasal cavity, the roof of the mouth, and the floor of the
orbit; it enters into the formation of two fossae, the pterygopalatine
and pterygoid fossae; and one fissure,
the inferior orbital fissure. The palatine bone somewhat resembles the
letter L, and consists of a horizontal and a vertical part and three
outstanding processes—viz., the pyramidal process, which is directed backward
and lateralward from the junction of the two parts,
and the orbital and sphenoidal processes, which
surmount the vertical part, and are separated by a deep notch, the sphenopalatine notch.
The Horizontal Part (pars horizontalis;
horizontal plate).—The horizontal part is
quadrilateral, and has two surfaces and four borders.
Surfaces.—The superior surface,
concave from side to side, forms the back part of the floor of the nasal
cavity. The inferior surface, slightly concave and rough, forms, with
the corresponding surface of the opposite bone, the posterior fourth of the
hard palate. Near its posterior margin may be seen a more or less marked
transverse ridge for the attachment of part of the aponeurosis
of the Tensor veli palatini.
Left palatine bone. Nasal aspect. Enlarged.
Left palatine bone. Posterior aspect. Enlarged
Borders.—The anterior border is
serrated, and articulates with the palatine process of the maxilla. The posterior
border is concave, free, and serves for the attachment of the soft palate.
Its medial end is sharp and pointed, and, when united with that of the opposite
bone, forms a projecting process, the posterior nasal spine for the
attachment of the Musculus uvulae. The lateral
border is united with the lower margin of the perpendicular part, and is
grooved by the lower end of the pterygopalatine
canal. The medial border, the thickest, is serrated for articulation
with its fellow of the opposite side; its superior edge is raised into a ridge,
which, united with the ridge of the opposite bone, forms the nasal crest
for articulation with the posterior part of the lower edge of the vomer.
The Vertical Part (pars perpendicularis;
perpendicular plate)—The vertical part is
thin, of an oblong form, and presents two surfaces and four borders.
Surfaces.—The nasal surface exhibits
at its lower part a broad, shallow depression, which forms part of the inferior
meatus of the nose. Immediately above this is a well-marked horizontal ridge,
the conchal crest, for articulation
with the inferior nasal concha; still higher is a second broad, shallow
depression, which forms part of the middle meatus, and is limited above by a
horizontal crest less prominent than the inferior, the ethmoidal
crest, for articulation with the middle nasal concha. Above the ethmoidal crest is a narrow, horizontal groove, which forms
part of the superior meatus.
The maxillary surface is rough and irregular
throughout the greater part of its extent, for articulation with the nasal
surface of the maxilla; its upper and back part is smooth where it enters into
the formation of the pterygopalatine fossa; it is
also smooth in front, where it forms the posterior part of the medial wall of
the maxillary sinus. On the posterior part of this surface is a deep vertical
groove, converted into the pterygopalatine
canal, by articulation with the maxilla; this canal transmits the
descending palatine vessels, and the anterior palatine nerve.
Borders.—The anterior border is thin
and irregular; opposite the conchal crest is a
pointed, projecting lamina, the maxillary process, which is directed
forward, and closes in the lower and back part of the opening of the maxillary
sinus. The posterior border presents a deep groove, the edges of which
are serrated for articulation with the medial pterygoid
plate of the sphenoid. This border is continuous above with the sphenoidal process; below it expands into the pyramidal
process. The superior border supports the orbital process in front and
the sphenoidal process behind. These processes are
separated by the sphenopalatine notch,
which is converted into the sphenopalatine
foramen by the under surface of the body of the sphenoid. In the
articulated skull this foramen leads from the pterygopalatine
fossa into the posterior part of the superior meatus of the nose, and transmits
the sphenopalatine vessels and the superior nasal and
nasopalatine nerves. The inferior border is
fused with the lateral edge of the horizontal part, and immediately in front of
the pyramidal process is grooved by the lower end of the pterygopalatine
canal.
The Pyramidal Process or Tuberosity (processus
pyramidalis).—The pyramidal process projects
backward and lateralward from the junction of the
horizontal and vertical parts, and is received into the angular interval
between the lower extremities of the pterygoid
plates. On its posterior surface is a smooth, grooved, triangular area,
limited on either side by a rough articular furrow. The furrows articulate with
the pterygoid plates, while the grooved intermediate
area completes the lower part of the pterygoid fossa
and gives origin to a few fibers of the Pterygoideus internus. The
anterior part of the lateral surface is rough, for articulation with the
tuberosity of the maxilla; its posterior part consists of a smooth triangular
area which appears, in the articulated skull, between the tuberosity of the
maxilla and the lower part of the lateral pterygoid
plate, and completes the lower part of the infratemporal
fossa. On the base of the pyramidal process, close to its union with the
horizontal part, are the lesser palatine foramina for the transmission of the
posterior and middle palatine nerves.
The Orbital Process (processus orbitalis).—The
orbital process is placed on a higher level than the sphenoidal,
and is directed upward and lateralward from the front
of the vertical part, to which it is connected by a constricted neck. It
presents five surfaces, which enclose an air cell. Of these surfaces, three are
articular and two non-articular. The articular surfaces are: (1) the anterior
or maxillary, directed forward, lateralward,
and downward, of an oblong form, and rough for articulation with the maxilla;
(2) the posterior or sphenoidal,
directed backward, upward, and medialward; it
presents the opening of the air cell, which usually communicates with the sphenoidal sinus; the margins of the opening are serrated
for articulation with the sphenoidal concha; (3) the medial
or ethmoidal, directed forward,
articulates with the labyrinth of the ethmoid. In
some cases the air cell opens on this surface of the bone and then communicates
with the posterior ethmoidal cells. More rarely it
opens on both surfaces, and then communicates with the posterior ethmoidal cells and the sphenoidal
sinus. The non-articular surfaces are: (1) the superior or orbital,
directed upward and lateralward; it is triangular in
shape, and forms the back part of the floor of the orbit; and (2) the lateral,
of an oblong form, directed toward the pterygopalatine
fossa; it is separated from the orbital surface by a rounded border, which
enters into the formation of the inferior orbital fissure.
The Sphenoidal Process (processus
sphenoidalis).—The
sphenoidal process is a thin, compressed plate, much
smaller than the orbital, and directed upward and medialward.
It presents three surfaces and two borders. The superior surface
articulates with the root of the pterygoid process
and the under surface of the sphenoidal concha, its
medial border reaching as far as the ala of the vomer; it presents a groove which contributes to the
formation of the pharyngeal canal. The medial surface is concave, and
forms part of the lateral wall of the nasal cavity. The lateral surface
is divided into an articular and a non-articular portion: the former is rough,
for articulation with the medial pterygoid plate; the
latter is smooth, and forms part of the pterygopalatine
fossa. The anterior border forms the posterior boundary of the sphenopalatine notch. The posterior border, serrated
at the expense of the outer table, articulates with the medial pterygoid plate.
The orbital and sphenoidal
processes are separated from one another by the sphenopalatine
notch. Sometimes the two processes are united above, and form between them
a complete foramen, or the notch may be crossed by one or more spicules of
bone, giving rise to two or more foramina.
Ossification.—The palatine bone is
ossified in membrane from a single center, which
makes its appearance about the sixth or eighth week of fetal
life at the angle of junction of the two parts of the bone. From this point
ossification spreads medialward to the horizontal
part, downward into the pyramidal process, and upward into the vertical part.
Some authorities describe the bone as ossifying from four centers:
one for the pyramidal process and portion of the vertical part behind the pterygopalatine groove; a second for the rest of the
vertical and the horizontal parts; a third for the orbital, and a fourth for
the sphenoidal process. At the time of birth the
height of the vertical part is about equal to the transverse width of the
horizontal part, whereas in the adult the former measures about twice as much
as the latter.
Articulations.—The palatine
articulates with six bones: the sphenoid, ethmoid,
maxilla, inferior nasal concha, vomer, and opposite
palatine.
Theme 3. nasal,
lacrimal, zygomatic bone, inferior nasal concha, vomer, mandible, hyoid bone
Nasal
bone (paired) forms bony part of nasal dorsum.
Articulation of nasal and lacrimal bones with maxilla.
Lacrimal
bones (paired) forms anterior part of the medial orbital wall.
Zygomatic
bone (paired) has frontal and temporal processes; lateral, temporal and orbital
surfaces.
Left zygomatic bone in situ
The zygomatic bone is small and
quadrangular, and is situated at the upper and lateral part of the face: it
forms the prominence of the cheek, part of the lateral wall and floor of the
orbit, and parts of the temporal and infratemporal
fossae. It presents a malar and a
temporal surface; four processes, the frontosphenoidal,
orbital, maxillary, and temporal; and four borders.
Surfaces.—The malar surface is convex
and perforated near its center by a small aperture,
the zygomaticofacial foramen, for the
passage of the zygomaticofacial nerve and vessels;
below this foramen is a slight elevation, which gives origin to the Zygomaticus.
The temporal surface directed backward and medialward, is concave, presenting medially a rough,
triangular area, for articulation with the maxilla, and laterally a smooth,
concave surface, the upper part of which forms the anterior boundary of the
temporal fossa, the lower a part of the infratemporal
fossa. Near the center of this surface is the zygomaticotemporal foramen for the
transmission of the zygomaticotemporal nerve.
Processes.—The frontosphenoidal process is thick and
serrated, and articulates with the zygomatic process
of the frontal bone. On its orbital surface, just within the orbital margin and
about
Left zygomatic bone. Malar surface.
Left zygomatic bone. Temporal surface.
Borders.—The antero-superior
or orbital border is smooth, concave, and forms a considerable part of
the circumference of the orbit. The antero-inferior
or maxillary border is rough, and bevelled at the expense of its inner
table, to articulate with the maxilla; near the orbital margin it gives origin
to the Quadratus labii superioris. The postero-superior
or temporal border, curved like an italic letter f, is continuous
above with the commencement of the temporal line, and below with the upper
border of the zygomatic arch; the temporal fascia is
attached to it. The postero-inferior or
zygomatic border affords attachment by
its rough edge to the Masseter.
Ossification.
—The zygomatic bone is generally
described as ossifying from three centers—one for the
malar and two for the orbital portion; these appear about the eighth week and
fuse about the fifth month of fetal life. Mall
describes it as being ossified from one center which
appears just beneath and to the lateral side of the orbit. After birth, the
bone is sometimes divided by a horizontal suture into an upper larger, and a
lower smaller division. In some quadrumana the zygomatic bone consists of two parts, an orbital and a
malar.
Articulations.—The zygomatic articulates with four bones: the frontal, sphenoidal, temporal, and maxilla.
Vomer
(unpaired) is located in nasal cavity and forms bony septum nasi
with perpendicular lamina (ethmoid bone).
Mandible
(unpaired) has a body and two rami. There is alveolar arch with teeth alveoli.
Mandibular angle is located between, body and rami and it carries masseteric and pterygoid tuberosities for attachment of mastication muscles. Ramus
contains coronal and condilar processes. Mandibular
canal starts on the inner surface of the ramus and terminates by mental foramen
in body. It contains vessels and nerves that supply teeth in the lower jaw.
This is only bone that form synovial joint.
The Mandible, the largest and strongest bone of the face, serves for the
reception of the lower teeth. It consists of a curved, horizontal portion, the body,
and two perpendicular portions, the rami, which unite with the ends of
the body nearly at right angles.
The Body (corpus mandibulae).—The body is curved somewhat like a horseshoe and has two surfaces and
two borders.
Surfaces.—The external surface is
marked in the median line by a faint ridge, indicating the symphysis
or line of junction of the two pieces of which the bone is composed at an early
period of life. This ridge divides below and encloses a triangular eminence,
the mental protuberance, the base of which is depressed in the center but raised on either side to form the mental
tubercle. On either side of the symphysis, just
below the incisor teeth, is a depression, the incisive fossa, which
gives origin to the Mentalis and a small portion of
the Orbicularis oris. Below the second premolar
tooth, on either side, midway between the upper and lower borders of the body,
is the mental foramen, for the passage of the mental vessels and nerve.
Running backward and upward from each mental tubercle is a faint ridge, the oblique
line, which is continuous with the anterior border of the ramus; it affords
attachment to the Quadratus labii
inferioris and Triangularis;
the Platysma is attached below it.
Mandible. Outer surface. Side view
The internal surface is concave from side to side.
Near the lower part of the symphysis is a pair of
laterally placed spines, termed the mental spines, which give origin to
the Genioglossi. Immediately below these is a second
pair of spines, or more frequently a median ridge or impression, for the origin
of the Geniohyoidei. In some cases the mental spines
are fused to form a single eminence, in others they are absent and their
position is indicated merely by an irregularity of the surface. Above the
mental spines a median foramen and furrow are sometimes seen; they mark the
line of union of the halves of the bone. Below the mental spines, on either
side of the middle line, is an oval depression for the attachment of the
anterior belly of the Digastricus. Extending upward
and backward on either side from the lower part of the symphysis
is the mylohyoid line, which gives
origin to the Mylohyoideus; the posterior part of
this line, near the alveolar margin, gives attachment to a small part of the
Constrictor pharyngis superior, and to the pterygomandibular raphé.
Above the anterior part of this line is a smooth triangular area against which
the sublingual gland rests, and below the hinder part, an oval fossa for the submaxillary gland.
Borders.—The superior or alveolar
border, wider behind than in front, is hollowed into cavities, for the
reception of the teeth; these cavities are sixteen in number, and vary in depth
and size according to the teeth which they contain. To the outer lip of the
superior border, on either side, the Buccinator is
attached as far forward as the first molar tooth. The inferior border is
rounded, longer than the superior, and thicker in front than behind; at the
point where it joins the lower border of the ramus a shallow groove; for the
external maxillary artery, may be present.
Mandible. Inner surface. Side view
The Ramus (ramus mandibulae;
perpendicular portion).—The ramus is quadrilateral in shape, and has
two surfaces, four borders, and two processes.
Surfaces.—The lateral surface is flat
and marked by oblique ridges at its lower part; it gives attachment throughout
nearly the whole of its extent to the Masseter. The medial surface
presents about its center the oblique mandibular
foramen, for the entrance of the inferior alveolar vessels and nerve. The
margin of this opening is irregular; it presents in front a prominent ridge,
surmounted by a sharp spine, the lingula mandibulae, which gives attachment to the sphenomandibular ligament; at its lower and back part is a
notch from which the mylohyoid groove
runs obliquely downward and forward, and lodges the mylohyoid
vessels and nerve. Behind this groove is a rough surface, for the insertion of
the Pterygoideus internus.
The mandibular canal runs obliquely downward and forward in the ramus,
and then horizontally forward in the body, where it is placed under the alveoli
and communicates with them by small openings. On arriving at the incisor teeth,
it turns back to communicate with the mental foramen, giving off two small
canals which run to the cavities containing the incisor teeth. In the posterior
two-thirds of the bone the canal is situated nearer the internal surface of the
mandible; and in the anterior third, nearer its external surface. It contains
the inferior alveolar vessels and nerve, from which branches are distributed to
the teeth. The lower border of the ramus is thick, straight, and
continuous with the inferior border of the body of the bone. At its junction
with the posterior border is the angle of the mandible, which may be
either inverted or everted and is marked by rough,
oblique ridges on each side, for the attachment of the Masseter laterally, and
the Pterygoideus internus
medially; the stylomandibular ligament is attached to
the angle between these muscles. The anterior border is thin above,
thicker below, and continuous with the oblique line. The posterior border
is thick, smooth, rounded, and covered by the parotid gland. The upper
border is thin, and is surmounted by two processes, the coronoid in
front and the condyloid behind, separated by a
deep concavity, the mandibular notch.
The Coronoid Process (processus
coronoideus) is a thin, triangular eminence,
which is flattened from side to side and varies in shape and size. Its anterior
border is convex and is continuous below with the anterior border of the
ramus; its posterior border is concave and forms the anterior boundary
of the mandibular notch. Its lateral surface is smooth, and affords
insertion to the Temporalis and Masseter. Its medial surface gives
insertion to the Temporalis, and presents a ridge which begins near the apex of
the process and runs downward and forward to the inner side of the last molar
tooth. Between this ridge and the anterior border is a grooved triangular area,
the upper part of which gives attachment to the Temporalis, the lower part to
some fibers of the Buccinator.
The Condyloid Process
(processus condyloideus)
is thicker than the coronoid, and consists of two portions: the condyle,
and the constricted portion which supports it, the neck. The condyle
presents an articular surface for articulation with the articular disk of the temporomandibular joint; it is convex from before backward
and from side to side, and extends farther on the posterior than on the
anterior surface. Its long axis is directed medialward
and slightly backward, and if prolonged to the middle line will meet that of
the opposite condyle near the anterior margin of the foramen magnum. At the
lateral extremity of the condyle is a small tubercle for the attachment of the temporomandibular ligament. The neck is flattened
from before backward, and strengthened by ridges which descend from the
forepart and sides of the condyle. Its posterior surface is convex; its
anterior presents a depression for the attachment of the Pterygoideus
externus.
The mandibular notch, separating the two processes,
is a deep semilunar depression, and is crossed by the masseteric
vessels and nerve.
Ossification.—The mandible is ossified
in the fibrous membrane covering the outer surfaces of Meckel’s
cartilages. These cartilages form the cartilaginous bar of the mandibular arch
, and are two in number, a right and a left. Their proximal or cranial ends are
connected with the ear capsules, and their distal extremities are joined to one
another at the symphysis by mesodermal tissue. They
run forward immediately below the condyles and then, bending downward, lie in a
groove near the lower border of the bone; in front of the canine tooth they
incline upward to the symphysis. From the proximal
end of each cartilage the malleus and incus, two of the bones of the middle
ear, are developed; the next succeeding portion, as far as the lingula, is replaced by fibrous tissue, which persists to
form the sphenomandibular ligament. Between the lingula and the canine tooth the cartilage disappears,
while the portion of it below and behind the incisor teeth becomes ossified and
incorporated with this part of the mandible.
Ossification takes place in the membrane covering the outer
surface of the ventral end of Meckel’s cartilage and
each half of the bone is formed from a single center
which appears, near the mental foramen, about the sixth week of fetal life. By the tenth week the portion of Meckel’s cartilage which lies below and behind the incisor
teeth is surrounded and invaded by the membrane bone. Somewhat later, accessory
nuclei of cartilage make their appearance, viz., a wedge-shaped nucleus in the condyloid process and extending downward through the ramus;
a small strip along the anterior border of the coronoid process; and smaller
nuclei in the front part of both alveolar walls and along the front of the
lower border of the bone. These accessory nuclei possess no separate ossific centers, but are invaded
by the surrounding membrane bone and undergo absorption. The inner alveolar
border, usually described as arising from a separate ossific
center (splenial center), is formed in the human mandible by an ingrowth
from the main mass of the bone. At birth the bone consists of two parts, united
by a fibrous symphysis, in which ossification takes
place during the first year.
The foregoing description of the ossification of the
mandible is based on the researches of Low 44 and Fawcett, 45 and differs somewhat from that usually given.
Articulations.—The mandible
articulates with the two temporal bones.
At birth
Changes Produced in the Mandible by AgeAt
birth the body of the bone is a mere shell,
containing the sockets of the two incisor, the canine, and the two deciduous
molar teeth, imperfectly partitioned off from one another. The mandibular canal
is of large size, and runs near the lower border of the bone; the mental
foramen opens beneath the socket of the first deciduous molar tooth. The angle
is obtuse (175°), and the condyloid portion is nearly
in line with the body. The coronoid process is of comparatively large size, and
projects above the level of the condyle.
In childhood
In the adult.
In old age.
Side view of the
mandible at different periods of life.
After birth the two segments of the bone become
joined at the symphysis, from below upward, in the
first year; but a trace of separation may be visible in the beginning of the
second year, near the alveolar margin. The body becomes elongated in its whole
length, but more especially behind the mental foramen, to provide space for the
three additional teeth developed in this part. The depth of the body increases
owing to increased growth of the alveolar part, to afford room for the roots of
the teeth, and by thickening of the subdental portion
which enables the jaw to withstand the powerful action of the masticatory muscles;
but the alveolar portion is the deeper of the two, and, consequently, the chief
part of the body lies above the oblique line. The mandibular canal, after the
second dentition, is situated just above the level of the mylohyoid
line; and the mental foramen occupies the position usual to it in the adult.
The angle becomes less obtuse, owing to the separation of the jaws by the
teeth; about the fourth year it is 140°.
In the adult the alveolar and subdental
portions of the body are usually of equal depth. The mental foramen opens
midway between the upper and lower borders of the bone, and the mandibular
canal runs nearly parallel with the mylohyoid line.
The ramus is almost vertical in direction, the angle measuring from 110° to
120°.
In old age the bone becomes greatly reduced in size,
for with the loss of the teeth the alveolar process is absorbed, and,
consequently, the chief part of the bone is below the oblique line. The
mandibular canal, with the mental foramen opening from it, is close to the alveolar
border. The ramus is oblique in direction, the angle measures about 140°, and
the neck of the condyle is more or less bent backward.
Inferior
nasal concha (paired) - thin plate that separate middle and
inferior nasal meatus.
Hyoid bone is
positioned in neck between mandible and larynx. It has body, large and mall horns.
References:
1.Gray`s
Anatomy. Lawrence H. Bannister, Martin M. Berry, Patricia Collins and others. Churchhill Livingstone, - 1999. 2092 p.
2.
W. Kahle, H. Leonhardt, W. Platzer. Colour atlas and
Textbook of Human Anatomy. –
3.
R.D. Lockhart, G.F. Hamilton, F.W. Fyfe. Anatomy of the human body. –
5. Synelnіkov R.D. The atlas of anatomy of the man. Іn the 4-th volumes. -: Medіcіna, 1991.
6. Lecture.
7. Colіn H. Wheatley, B.Kolz. Human
anatomy and physіology. 1995.
8. Reminetskyy B.Y., Fedonyuk Y.I. Human anatomy. Locomotory
apparatus. Notes. ‘Ukrmedknyha’, - 2002, - 136 p.