Skeletal System

Cranial Bones from Superior View.: When the external skull is viewed from the superior aspect, four cranial bones are visible (Figure 3-1). At the front of the skull is the single frontal bone (frunt-il). At each side of the skull is the paired parietal bone (pah-ri-it-al). At the back of the skull is the single occipital bone (ok-sip-it-al). This main division of the cranial bones of the skull is discussed later.

Skull Sutures from Superior View.: Sutures among these four cranial bones are also visible from the superior aspect are the coronal, sagittal, and lambdoidal (Figure 3-2; see Table 3-2). The suture extending across the skull, between the frontal bone and parietal bone, is the paired coronal suture (kor-oh-nahl). This is the location of the diamond-shaped anterior fontanelle or “soft spot” in a newborn where the two frontal and two parietal bones join, which generally remains open until two years of age.

A single suture, the sagittal suture (saj-i-tel), extends from the front to the back of the skull at the midline between the parietal bones; the sagittal suture is parallel with the sagittal plane of the skull. The coronal sutures and sagittal suture generally form a right angle with each other. Another single suture located between the occipital bone and the parietal bone, is the lambdoidal suture (lam-doid-al), which is by far more serrated-looking than the others, resembling an upside down V.

Facial Bones from Anterior View.: The facial bones on the anterior aspect of the skull include: lacrimal bone (lak-ri-mal), nasal bone (nay-zil), vomer (vo-mer), inferior nasal concha (kong-kah, plural, conchae [kong-kee]), zygomatic bone (zy-go-mat-ik), maxilla (mak-sil-ah), and mandible (man-di-bl) (Figure 3-4). The palatine bone (pal-ah-tine) is not visible on this view and is not strictly considered a facial bone by anatomists, but for ease of learning, it is included under the heading of facial bones. This main division of the facial bones of the skull is discussed later.

Orbit and Associated Structures from Anterior View.: The orbit (or-bit), which contains and protects the eyeball, is a prominent feature of the anterior part of the skull (Figure 3-5 and see Figure 2-6). Many skull bones form both the walls and apex of each of the orbits (Table 3-5). The larger orbital walls (or-bit-al) are composed of the orbital plates of the frontal bone (making the roof or superior wall), the ethmoid bone (forming the greatest part of the medial wall), the lacrimal bone (at the anterior medial corner of the orbit and orbital surfaces of the maxilla [the floor or inferior wall]), and the zygomatic bone (the anterior part of the lateral wall). The orbital surface of the greater wing of the sphenoid bone is also included (the posterior part of the lateral wall).

The orbital apex is the deepest part of the orbit and is composed of the lesser wing of the sphenoid bone (forming the base) and the palatine bone (a small inferior part) (Figure 3-6; see Table 3-5). The round opening in the orbital apex is the optic canal (op-tik), which lies between the two roots of the lesser wing of the sphenoid bone (see Table 3-3). The second cranial or optic nerve passes through the optic canal to reach the eyeball. The ophthalmic artery also extends through the canal to reach the eye.

Two orbital fissures are noted on the anterior aspect: the superior and inferior orbital fissures (Figure 3-7; see Table 3-3). Lateral to the optic canal is the curved and slitlike superior orbital fissure, between the greater and lesser wings of the sphenoid bone. Similar to the optic canal, the superior orbital fissure connects the orbit with the cranial cavity. The third cranial or oculomotor nerve, the fourth cranial or trochlear nerve, the sixth cranial or abducens nerve, and the ophthalmic nerve (or division from the fifth cranial or trigeminal nerve) and vein travel through this fissure (see Figures 8-8 and 8-9 ).

The inferior orbital fissure can also be seen between the greater wing of the sphenoid bone and the maxilla. The inferior orbital fissure connects the orbit with the infratemporal and pterygopalatine fossae (discussed later). The infraorbital and zygomatic nerves, branches of the maxillary nerve, and infraorbital artery enter the orbit through this fissure. The inferior ophthalmic vein travels through this fissure to join the pterygoid plexus of veins (see Figure 6-12).

Nasal Cavity and Associated Structures from Anterior View.: The nasal cavity (nay-zil) or nasal fossa can also be viewed on the skull from the anterior (Figure 3-8; see Figure 3-56 and Figure 2-7). The nasal cavity is the upper part of the respiratory tract and is located between the orbits. It has lateral walls and a floor, with anterior and posterior openings, and is mainly composed of both bone and cartilage.

The bridge of the nose is formed from the paired nasal bones (see Figure 3-40). The nasion, a midpoint landmark, is located at the junction of the frontal and nasal bones. The anterior opening of the nasal cavity, the piriform aperture (pir-i-form), is large and triangular. The anterior openings to the nasal cavities are the nares, and the posterior openings are choanae (or posterior nasal apertures).

The floor of the nasal cavity is formed from the bones of the hard palate: palatine processes of the maxillae anteriorly and the horizontal plates of the palatine bones posteriorly (see Figure 3-16). The lateral boundaries of the nasal cavity are also formed by the maxillae. Each lateral wall of the nasal cavity has three projecting structures that extend inward from the maxilla, which are the nasal conchae or turbinates. These are the superior, middle, and inferior nasal conchae. Each extends like a scroll into the nasal cavity. The superior nasal concha and middle nasal concha are formed from the ethmoid bone; the inferior nasal concha is a separate facial bone. Protected by each nasal concha is a channel, the nasal meatus (me-ate-us). Each meatus has openings through which the paranasal sinuses or nasolacrimal duct communicates with the nasal cavity.

The vertical partition or fin, the nasal septum, divides the nasal cavity into two parts (Figure 3-9 and see Figure 2-17). Although it is frequently deflected slightly to the left or right, in general the septum is aligned perpendicularly. Anteriorly, the nasal septum is formed by both the perpendicular plate of the ethmoid bone superiorly and the nasal septal cartilage inferiorly. The posterior parts of the nasal septum are formed by the vomer.

Cranial Bones from Lateral View.: The cranium is easily noted on the lateral aspect, including the following cranial bones: the occipital, frontal, parietal, temporal, sphenoid bone (sfe-noid), and ethmoid bone (eth-moid) (Figure 3-11). This main division of the bones of the skull is discussed later.

Skull Sutures from Lateral View.: Also noted on the lateral surface of the skull are the associated sutures of the cranial bones (see Figure 3-11 and Table 3-2). These sutures include the coronal suture, an articulation between the frontal bone and each parietal bone, and the lambdoidal suture, an articulation between the occipital bone and each parietal bone. Also present is the arched squamosal suture (skway-mus-al), between each temporal bone and parietal bone.

Skull Lines from Lateral View.: On the lateral surface of the skull are two separate parallel ridges or temporal lines (tem-poh-ral), crossing both the frontal and parietal bones (Figure 3-12). The superior ridge is the superior temporal line. The inferior ridge or inferior temporal line is the superior boundary of the temporal fossa where the fan-shaped temporalis muscle attaches (see Figure 4-22).

Skull Fossae from Lateral View.: The temporal fossa is easily seen on the lateral surface of the skull (Figure 3-13). The temporal fossa is formed by several bones of the skull and contains the body of the temporalis muscle. Inferior to the temporal fossa is the infratemporal fossa (in-frah-tem-poh-ral). Deep to the infratemporal fossa and more difficult to see is the pterygopalatine fossa (ter-i-go-pal-ah-tine). The temporal, infratemporal, and pterygopalatine fossae are discussed later and contain many important head and neck structures.

Zygomatic Arch and Temporomandibular Joint from Lateral View.: Farther inferior on the lateral aspect of the skull are many important bony landmarks (Figure 3-14). The zygomatic arch or cheekbone is visible, formed by the union of the broad temporal process of the zygomatic bone and the slender zygomatic process of the temporal bone (see Table 3-4 and see Figure 2-9). The suture between these two bones is the temporozygomatic suture (tem-por-oh-zi-go-mat-ik) (see Table 3-2). The zygomatic arch serves as the origin for the masseter muscle (see Figure 4-21).

The temporomandibular joint (TMJ) is also noted, which is a movable articulation between the temporal bone and the mandible (see Chapter 5). More specific landmarks of these bones are discussed later.

Hard Palate from Inferior View.: At the anterior part of the skull’s inferior surface is the hard palate, bordered by the alveolar process of the maxilla (al-vee-o-lar) with its maxillary teeth (Figure 3-16; see Figure 2-15 and Table 3-4). The hard palate is formed by the two palatine processes of the maxillae anteriorly and the two horizontal plates of the palatine bones posteriorly, an articulation which is noted by the prominent median palatine suture, which is noted clinically as the median palatine raphe (see Figure 2-15 and Table 3-2). The other suture is the transverse palatine suture, an articulation between the two palatine processes of the maxillae and the two horizontal plates of the palatine bones.

The hard palate forms the floor of the nasal cavity as well as the roof of the mouth. The posterior edge of the hard palate forms the inferior border of two funnel-shaped cavities, the posterior nasal apertures or choanae (ko-a-nay). The superior border of each aperture is formed by the vomer and the sphenoid bone. The posterior edge of the vomer forms the medial border of the posterior nasal apertures. The posterior nasal apertures are the posterior openings of the nasal cavity.

Near the superior border of each posterior nasal aperture is a small canal, the pterygoid canal (ter-i-goid) (see Table 3-3). The pterygoid canal extends to open into the pterygopalatine fossa and carries the pterygoid nerve and blood vessels (further discussion later).

Middle Part of Skull from Inferior View.: The middle part of the skull from the inferior view has many important surface prominences and depressions (Figure 3-17). The lateral borders of the posterior nasal apertures are formed on each side by the pterygoid process of the sphenoid bone (see Table 3-4).

Each pterygoid process consists of a thin medial pterygoid plate and a flattened lateral pterygoid plate. The depression between the medial and lateral plates is the pterygoid fossa. At the inferior part of the medial plate of the pterygoid process is a thin curved process, the hamulus (ham-u-lis). The sphenoid bone and its landmarks are discussed later.

External Skull Foramina from Inferior View.: The inferior surface of the external skull has a large number of foramina (Figure 3-18; see Table 3-3). These openings provide entrances and exits for the arteries and veins that supply the brain and facial tissue (see Chapter 6). They also allow the cranial nerves to pass to and from the brain (see Figure 8-5).

The larger anterior oval opening on the sphenoid bone is the foramen ovale (o-va-lee) for the mandibular nerve (or division) of the fifth cranial or trigeminal nerve (see Figure 8-7). The adjacent smaller and more posterior opening is the foramen spinosum (spine-o-sum), which carries the middle meningeal artery into the cranial cavity. The foramen spinosum receives its name from the nearby (angular) spine of the sphenoid bone, which is at the posterior extremity of the sphenoid bone.

Also on the external surface of the skull is the large, irregularly shaped foramen lacerum (lah-ser-um), which in life is filled with cartilage. Posterolateral to the foramen lacerum is a round opening in the petrous part of the temporal bone, the carotid canal (kah-rot-id). The carotid canal carries the internal carotid artery and sympathetic carotid plexus. A pointed bony projection, the styloid process (sty-loid), is visible lateral and posterior to the carotid canal (see Table 3-4). Immediately posterior to the styloid process is the stylomastoid foramen (sty-lo-mas-toid), an opening through which the seventh cranial or facial nerve exits from the skull to the face.

The jugular foramen (jug-you-lar), just medial to the styloid process, is more easily seen if the skull model is tilted to one side. The jugular foramen is the opening through which pass the internal jugular vein and three cranial nerves: the ninth cranial or glossopharyngeal nerve, the tenth cranial or vagus nerve, and the eleventh cranial or accessory nerve.

The largest opening on the inferior view is the foramen magnum (mag-num) of the occipital bone, through which the spinal cord, vertebral arteries, and eleventh cranial or accessory nerve pass.

Internal Skull Foramina from Superior View.: Also present on the superior surface of the internal skull are the inside openings of the optic canal, superior orbital fissure, foramen ovale, foramen spinosum, foramen lacerum, jugular foramen, and foramen magnum, as discussed before when viewing the external skull surface (see Figure 3-19; see Table 3-3). Additionally, many other foramina are present on the internal surface of the skull. The perforated cribriform plate (krib-ri-form), with foramina for the first cranial or olfactory nerve, and the foramen rotundum (row-tun-dum) for the maxillary nerve (or division) of the fifth cranial or trigeminal nerve are also seen from this view (see Figure 8-7).

Finally, also present are the hypoglossal canal (hi-poh-gloss-al) for the twelfth cranial or hypoglossal nerve and the internal acoustic meatus (ah-koos-tik) for the seventh cranial or facial nerve and the eighth cranial or vestibulocochlear nerve.

Occipital Bone from Inferior View.: On the external surface of the occipital bone from an inferior view, it can be seen that the foramen magnum is completely formed by this bone (Figure 3-22; see Table 3-3). Lateral and anterior to the foramen magnum are the paired occipital condyles, curved and smooth projections. The occipital condyles have a movable articulation with the atlas, the first cervical vertebra of the vertebral column (discussed later). On the stout basilar part (bas-i-lar), a four-sided plate anterior to the foramen magnum, is a midline projection, the pharyngeal tubercle (fah-rin-je-al).

When tilting the skull model, the openings anterior and lateral to the foramen magnum are visible on the inferior view of the occipital bone (see Table 3-3). These openings are the paired hypoglossal canals (see Figure 3-22). The twelfth cranial or hypoglossal nerve is transmitted through the hypoglossal canal. Also present is the jugular notch of the occipital bone, the medial part that forms the jugular foramen (the lateral part is from the temporal bone).

Frontal Bone from Anterior View.: On the anterior aspect, certain landmarks are visible on the frontal bone (Figure 3-24, see Figures 2-2 and 2-6 ). The orbital plate of the frontal bone forms the superior wall or orbital roof. The curved elevations over the superior part of the orbit are the supraorbital ridges, subjacent to the eyebrows, which are more prominent in adult males. The supraorbital notch (soo-prah-or-bit-al) is located on the medial part of the supraorbital ridge and is where the supraorbital artery and nerve travel from the orbit to the forehead. The supraorbital notch is located about 1 inch from the midline and can produce soreness when palpated.

Between the supraorbital ridges is the glabella, the smooth elevated area between the eyebrows, which tends to be flat in children and adult females, but forms a rounded prominence in adult males. The prominence of the forehead, the frontal eminence, is also evident. In contrast, the frontal eminence is usually more pronounced in children and adult females. Lateral to the orbit is a projection, the orbital surface of the zygomatic process of the frontal bone (see Table 3-4).

Frontal Bone from Inferior View.: From the inferior view of the frontal bone, each lacrimal fossa (lak-ri-mal) is visible (Figure 3-25 and see Figure 2-6). The lacrimal fossa is located just inside the lateral part of the supraorbital ridge. This fossa contains the lacrimal gland, which produces lacrimal fluid or tears (see Chapter 7). After lubricating the eye, the lacrimal fluid empties into the nasal cavity through the nasolacrimal duct.

Squamous Part of Temporal Bone.: In addition to helping form the braincase, the squamous part of the temporal bone forms the zygomatic process of the temporal bone, which forms a part of the zygomatic arch (Figure 3-29; see Table 3-4). This part of the temporal bone also forms the cranial part of the temporomandibular joint (see Chapter 5). On the inferior surface of the zygomatic process of the temporal bone is the articular fossa (ar-tik-you-ler) (see Figures 5-2 and 5-4 ).

Anterior to the articular fossa is the articular eminence, and posterior is the postglenoid process (post-gle-noid) (see Table 3-4). The articular fossa and eminence are parts of the temporal bone that articulate with the mandible at the temporomandibular joint, which is an important consideration for dental professionals.

Tympanic Part of Temporal Bone.: The tympanic part of the temporal bone forms most of the external acoustic meatus (ah-koos-tik), a short canal leading to the tympanic cavity, located posterior to the articular fossa (Figure 3-30; see Figure 2-4 and Table 3-3). Also, posterior to the articular fossa, the tympanic part is separated from the petrosal part by a fissure, the petrotympanic fissure (pe-troh-tim-pan-ik), through which the chorda tympani nerve emerges.

Petrous Part of Temporal Bone.: On the inferior aspect of the petrous part of the temporal bone and posterior to the external acoustic meatus is a large roughened projection, the mastoid process (mass-toid) (Figure 3-31; see Table 3-4). The mastoid process is composed of air spaces or mastoid air cells that communicate with the middle ear cavity and also serves as the site for attachment of the large muscles of the neck such as the sternocleidomastoid muscle (see Figure 4-1).

Medial to the mastoid process is the mastoid notch (see Figure 3-31). Inferior and medial to the external acoustic meatus is a long, pointed bony projection, the styloid process, a structure that serves for the attachment of tongue and pharyngeal muscles and ligaments (see Table 3-4). The stylomastoid foramen carries the seventh cranial or facial nerve and is named for its location between the styloid process and mastoid process (see Table 3-3).

The large circular aperture of the carotid canal is also noted, 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. When the skull model is tilted, the jugular notch of the temporal bone is visible (see Table 3-3), which is the lateral part that forms the jugular foramen (the medial part is from the occipital bone).

On the intracranial surface of the petrous part of the temporal bone is the internal acoustic meatus, which carries the eighth cranial or vestibulocochlear nerve and the seventh cranial or facial nerve (see Figure 3-19; see Table 3-3). The size of the internal acoustic meatus varies considerably; its margins are smooth and rounded, and it leads into a short canal, about 1 cm in length, which runs lateralward. Both of these cranial nerves enter the skull at the internal acoustic meatus from the brain. The vestibulocochlear nerve remains inside the petrous part of the temporal bone, which contains the inner ear. In contrast, the facial nerve takes a convoluted path through the bone, eventually emerging at the stylomastoid foramen.

Body of Sphenoid Bone.: The middle part is the body of the sphenoid bone, which articulates on its anterior surface with the ethmoid bone and posteriorly with the basilar part of the occipital bone (see Figures 3-32 and 3-33). The body contains the paired paranasal sinuses, the sphenoidal sinuses (discussed later).

Sphenoid Bone Processes.: The body of the sphenoid bone has three paired processes projecting from it: the lesser wing, the greater wing, and the pterygoid process (Figure 3-34; see Figures 3-32 and 3-33 and Table 3-4). The projections include an anterior process, the lesser wing of the sphenoid bone, which forms the base of the orbital apex, and a posterolateral process, the greater wing of the sphenoid bone (see Figures 3-5 and 3-6).

Inferior to the greater wing of the sphenoid bone is the pterygoid process, an area of attachment for some of the muscles of mastication. The pterygoid process consists of two plates that project inferiorly, the flattened lateral pterygoid plate and thinner medial pterygoid plate, with the pterygoid fossa between them (see Figure 3-17). The hamulus, a thin curved process, is the inferior termination of the medial pterygoid plate. The pterygomaxillary fissure is between the pterygoid process of the sphenoid bone and the maxillary tuberosity of the maxilla (see Figure 3-61).

A sharp, pointed area, the (angular) spine of the sphenoid bone, is located at the posterior corner of each greater wing of the sphenoid bone. Each greater wing is divided into two smaller surfaces by the infratemporal crest: the temporal and infratemporal surfaces. The infratemporal fossa is lateral to the lateral pterygoid plate.

Sphenoid Bone Foramina.: Many foramina and fissures are located in the sphenoid which carry nerves and blood vessels of the head and neck that are significant to dental professionals, such as the superior orbital fissure (with ophthalmic nerve), foramen rotundum (with maxillary nerve) and foramen ovale (with mandibular nerve) (see Figures 3-32 and 3-33; see Table 3-3).

Ethmoid Bone Plates and Associated Structures.: First to consider are the two unpaired plates that form the ethmoid bone: the midline vertical perpendicular plate (per-pen-dik-you-lar) and the horizontal cribriform plate, which it crosses. The perpendicular plate is easily seen in the nasal cavity and aids the nasal septal cartilage and vomer in forming the nasal septum (see Figure 3-35). A vertical midline continuation of the perpendicular plate superiorly into the cranial cavity is the wedge-shaped crista galli (kris-tah gal-lee), which serves as an attachment for layers covering the brain.

The cribriform plate, visible from the inside of the cranial cavity and present on the superior aspect of the bone and surrounding the cristal galli, is perforated by foramina to allow the passage of olfactory nerves for the sense of smell (Figures 3-36 and 3-37).

The lateral parts of the ethmoid bone form the superior nasal conchae (kong-kee) and middle nasal conchae in the nasal cavity and the paired orbital plates (Figure 3-38; see Figure 3-37). The orbital plate of the ethmoid bone forms the medial orbital wall. Between the orbital plate and the conchae are the ethmoidal sinuses or ethmoid air cells, which are a variable number of small cavities in the lateral mass of the ethmoid (discussed later).

Zygomatic Bone Processes.: Each process of the zygomatic bone forms important structures of the skull (see Figures 3-41 and 3-42 and Table 3-4). The orbital surface of the frontal process of the zygomatic bone forms the anterior lateral orbital wall, with usually a small paired foramen, the zygomaticofacial foramen (zy-go-mat-i-ko-fay-shal) opening on its lateral surface (see Table 3-3). The temporal process of the zygomatic bone forms the zygomatic arch along with the zygomatic process of the temporal bone, with a paired zygomaticotemporal foramen (zy-go-mat-i-ko-tem-poh-ral) present on the surface of the bone (see Table 3-3). The orbital surface of the maxillary process of the zygomatic bone forms a part of the infraorbital rim (in-frah-or-bit-al) and a small part of the anterior part of the lateral orbital wall.

Plates and Sutures of Palatine Bones.: Both the horizontal and vertical plates can be seen from a posterior view of a palatine bone (Figure 3-43). The horizontal plates of the palatine bone form the lesser or posterior part of the hard palate. The vertical plates of the palatine bone form a part of the lateral walls of the nasal cavity, and each plate contributes a small lip of bone to the orbital apex.

The palatine bones serve as a link between the maxillae and the sphenoid bone with which they articulate, as well as with each other. The two horizontal plates articulate with each other at the posterior part of the median palatine suture and more anteriorly with the maxillae at the transverse palatine suture (Figure 3-44; see Table 3-2 and Figure 2-15).

Foramina of Palatine Bones.: There are two important foramina in the palatine bones that transmit nerves and blood vessels to this region: the greater and lesser palatine (see Figure 3-44 and Table 3-3). The larger greater palatine foramen is located in the posterolateral region of each of the palatine bones, usually at the apex of the maxillary third molar. The greater palatine foramen transmits the greater palatine nerve and blood vessels and is a landmark for the administration of the greater palatine block (see Figure 9-19).

A smaller opening nearby, the lesser palatine foramen, transmits the lesser palatine nerve and blood vessels to the soft palate and tonsils. Both foramina are openings of the pterygopalatine canal that carries the descending palatine nerves and blood vessels from the pterygopalatine fossa to the palate.

The sphenopalatine foramen (sfe-no-pal-ah-tine) is the opening between the sphenoid bone and orbital processes of the palatine bone; it opens into the nasal cavity and gives passage to branches from the pterygopalatine ganglion and the sphenopalatine artery from the maxillary artery.

Maxillae from Anterior View.: From the anterior view, each frontal process of the maxilla articulates with the frontal bone and forms the medial orbital rim with the lacrimal bone on its anterior surface (Figures 3-46 and 3-47; see Figure 3-45 and Table 3-4). Each maxilla’s orbital surface is separated from the sphenoid bone by the inferior orbital fissure (see Figure 3-7 and Table 3-3). The inferior orbital fissure carries the infraorbital and zygomatic nerves, infraorbital artery, and inferior ophthalmic vein. The groove in the floor of the orbital surface is the infraorbital sulcus.

The infraorbital sulcus becomes the infraorbital canal and then terminates on the facial surface of each maxilla as the infraorbital foramen (see Table 3-3). It is located approximately 2 cm inferior to the midpoint of the inferior margin of the orbit, in a vertical line with the supraorbital notch, which is superior to it. This foramen transmits the infraorbital nerve and blood vessels. The infraorbital foramen is a landmark for the administration of the infraorbital block (see Figure 9-15). Palpation of the infraorbital foramen during an extraoral examination or an administration of a local anesthetic agent will cause soreness to the area. Inferior to the infraorbital foramen is an elongated depression, the canine fossa (kay-nine). The canine fossa is just posterosuperior to the roots of each of the maxillary canine teeth.

Each tooth of the maxillary arch is covered by a prominent facial ridge of bone, a part of the alveolar process of the maxilla (see Table 3-4). The facial ridge over each of the maxillary canines, the canine eminence, is especially prominent, making it a landmark for the administration of the anterior superior alveolar block (see Figure 9-12). The maxillary bone over the facial surface of the maxillary teeth is less dense than the mandibular bone over similar teeth as can be viewed on a panoramic radiograph (see Figures 3-46 and 3-50). This allows a greater incidence of clinically adequate local anesthesia for the maxillary teeth when the agent is administered as a local infiltration than would occur with similar teeth on the mandibular arch (see Chapter 9).

Maxilla from Lateral View.: From the lateral view, each zygomatic process of the maxilla articulates with the zygomatic bone laterally, completing the infraorbital rim (see Figures 3-46 and 3-47 and Table 3-4). Some of the landmarks noted from the anterior view of the maxilla are also present.

On the posterior part of the body of the maxilla is a rounded, roughened elevation, the maxillary tuberosity, just posterior to the most distal molar of the maxillary arch of the dentition, which is a landmark for mounting radiographs as well serving as the one of the boundaries of the fossae of the skull (see Figures 3-46 to 3-48, 3-61 and 2-21). The superolateral part of the maxillary tuberosity is perforated by the posterior superior alveolar foramina, where the posterior superior alveolar nerve and blood vessel branches enter the bone from the posterior. The maxillary tuberosity and posterior superior alveolar foramina are also landmarks for the administration of the posterior superior alveolar block (see Figure 9-2).

Maxillae from Inferior View.: On the inferior aspect, each palatine process of the maxilla articulates with the other to form the major or anterior part of the hard palate (Figure 3-48; see Figure 3-46 and Table 3-4). There are a number of small pores in the maxillary bone of the anterior hard palate. The suture between these two palatine processes of the maxilla is the anterior part of the median palatine suture (see Table 3-2). This is covered by the median palatine raphe, a midline fibrous band of tissue, which is a landmark along with the hard palate pores for the administration of the anterior middle superior alveolar block (see Figures 2-15 and 9-28 ). On the posterior part of the body of the maxilla, the maxillary tuberosity is again viewed.

In the anterior midline between the articulating palatine processes of the maxillae, just posterior to the maxillary central incisors, is the incisive foramen (in-sy-ziv) (see Table 3-3). This foramen carries the branches of both the right and left nasopalatine nerves and blood vessels from the nasal cavity to the anterior hard palate. The soft tissue that bulges over the incisive foramen is the incisive papilla (see Figure 2-15). The incisive foramen and incisive papilla are landmarks for the administration of the nasopalatine block (see Figure 9-23).

The alveolar process of the maxilla usually contains the roots of the maxillary teeth (see Figures 3-46, 48, and 2-13 and Table 3-4). The alveolar process of the maxilla can become resorbed when completely edentulous in the maxillary arch (resorption occurs to a lesser extent in partially edentulous cases), possibly leading to problems with the maxillary sinuses (discussed later). However, the more superior body of the maxilla is not resorbed with tooth loss, but its walls may become thinner in this case.

The density of the maxillary bone in an area determines the route that a dental infection takes with abscess and fistula formation (see Chapter 12). In addition, the differences in alveolar process density determine the easiest and most convenient areas of bony fracture used if needed during tooth extraction. Thus the maxillary teeth are easier to remove by fracturing the thinner facial surface rather than the thicker lingual surface.

Mandible from Anterior View.: From the anterior view, there are many important landmarks such as the mental protuberance, the bony prominence of the chin, located inferior to the roots of the mandibular incisors (Figure 3-50; see Figure 2-22). The mental protuberance is more pronounced in males but can be visualized and palpated in females. In the midline on the anterior surface of the mandible is a faint ridge, an indication of the mandibular symphysis (sim-fi-sis), where the bone is formed by the fusion of right and left processes during mandibular development. Like other symphyses in the body, this is a midline articulation where the bones are joined by fibrocartilage, but this articulation fuses together in early childhood.

Farther posteriorly on the lateral surface of the mandible, usually inferior to the apices of the mandibular first and second premolars, is an opening, the mental foramen (see Figures 3-50 to 3-52 and Table 3-3). As mandibular growth proceeds in young children, the mental foramen alters in direction of its opening from anterior to posterosuperior. The mental foramen allows the entrance of the mental nerve and blood vessels into the mandibular canal (discussed later).

The mental foramen’s posterosuperior opening in adults signifies the changed direction of the emerging mental nerve. This is an important landmark to note intraorally and on a radiograph before administration of both mental and incisive blocks (see Figures 9-42 and 9-46). Not confusing the circular radiolucent mental foramen on a radiograph with a periapical lesion related to the teeth or any other oral radiolucent lesions is also important.

The heavy horizontal part of the lower jaw inferior to the mental foramen is the body of the mandible or base (see Figure 3-51). Superior to this, the part of the lower jaw that usually contains the roots of the mandibular teeth is the alveolar process of the mandible (see Figures 2-13 and 3-52 and Table 3-4). The body of the mandible, along with the alveolar process, elongates to provide space for additional teeth as the child nears adulthood.

The mandibular alveolar process can become resorbed when completely edentulous in the mandibular arch (occasionally noted also in partially edentulous cases). This resorption can occur to such an extent that the mental foramen is virtually on the superior border of the mandible, instead of opening on the anterior surface, changing its relative position. However, the more inferior body of the mandible is not affected and remains thick and rounded.

The alveolar process of the mandibular incisors is less dense than the body of the mandible and even less dense than the alveolar process of the mandibular posterior teeth as can be viewed on a panoramic radiograph (see Figures 3-46 and 3-50). This allows a local infiltration of local anesthetic agent for the mandibular anterior teeth to have a higher degree of success than the mandibular posterior teeth but always less success than all the maxillary teeth (see Chapter 9).

The density of the mandibular bone in an area also determines the route that a dental infection takes with abscess and fistula formation (see Chapter 12). In addition, the differences in alveolar process density determine the easiest and most convenient areas of bony fracture used during tooth extraction. Thus the mandibular third molar is easier to remove by fracturing the thinner lingual surface (being careful of nearby lingual nerve) rather than the thicker buccal surface, if needed.

Mandible from Lateral View.: On the lateral aspect of the mandible, the stout, flat plate(s) of the ramus (plural, rami) (ray-mus, ray-me) extends superiorly and posteriorly from the body of the mandible on each side (see Figure 3-52). During growth of the body, both the body of the mandible and alveolar process elongate posterior to the mental foramen, providing space for three additional permanent teeth. Each ramus, which serves as the primary area for the attachment of the muscles of mastication, grows superiorly and posteriorly, displacing the mental protuberance of the chin inferiorly and anteriorly nearing adulthood.

The anterior border of the ramus is a thin, sharp margin that terminates in the coronoid process (kor-ah-noid) (see Table 3-4). The main part of the anterior border of the ramus forms a concave forward curve, the coronoid notch. This notch is the greatest depression on the anterior border of the ramus. The coronoid notch is a landmark for the administration of the inferior alveolar block (see Figures 9-35 and 9-37). Inferior to the coronoid notch, the anterior border of the ramus becomes the external oblique line (ob-leek), a crest where the ramus joins the body of the mandible. The line is noted as a radiopaque line on a radiograph superior to the mylohyoid line; clinicians may use this line intraorally to help locate the coronoid notch (see Figure 3-50).

The posterior border of the ramus is thicker and extends from the angle of the mandible, which is the juncture between the ramus and the body of the mandible, to a large more posterior projection, the condyloid process (kon-di-loid), which consists of two parts: the mandibular condyle, and the constricted part which supports it, the neck (see Figures 3-50 to 3-53 and Table 3-4). The anteromedial border of the mandibular condylar neck is a landmark for the Gow-Gates mandibular block (see Figure 9-48). The articulating surface of the condyle (ar-tik-you-late-ing) is an oval head of the condyle involved in the temporomandibular joint (see Figure 5-3). Between the coronoid process and the condyle is a depression, the mandibular notch or sigmoid notch.

Mandible from Medial View.: Visible on the medial view of the mandible are the body of the mandible, the alveolar process of the mandible (see Table 3-4), and the ramus (Figure 3-54). In addition, near the midline of the mandible are the genial tubercles (ji-ni-il) or mental spines, a cluster of small projections that serve as a muscle attachment area.

At the lateral edge of each mandibular alveolar process is a rounded, roughened area, the retromolar triangle (re-tro-moh-lar), just posterior to the most distal molar of the mandibular arch of the dentition. The retromolar triangle is a bony landmark that, when covered with soft tissue, is the retromolar pad (see Figure 2-21).

Along each medial surface of the body of the mandible is the internal oblique ridge or mylohyoid line (my-lo-hi-oid) that extends posteriorly and superiorly, becoming more prominent as it ascends each body. The mylohyoid line is the point of attachment of the mylohyoid muscle that forms the floor of the mouth (see Figure 4-24). The roots of the mandibular posterior teeth often extend internally inferior to the mylohyoid line. The line can be noted on a radiograph as the radiopaque line inferior to the external oblique line (see Figure 3-50).

A shallow depression, the sublingual fossa (sub-ling-gwal), which contains the sublingual salivary gland, is located superior to the anterior part of the mylohyoid line (see Figure 7-7). Inferior to the posterior part of the mylohyoid line and inferior to the mandibular posterior teeth is a deeper depression, the submandibular fossa (sub-man-dib-you-lar), which contains the submandibular salivary gland (see Figure 7-5).

On the medial surface of the ramus is the mandibular foramen (man-dib-you-lar), which is the opening of the mandibular canal (see Figure 3-54 and Table 3-3). The mandibular foramen is three fourths the distance from the coronoid notch to the posterior border of the ramus (see Figure 9-35). The inferior alveolar nerve and blood vessels exit the mandible through the mandibular foramen after traveling in the mandibular canal. With age and tooth loss, the alveolar process is absorbed so that the mandibular canal becomes nearer the superior border. Sometimes with excessive alveolar process absorption, the mandibular canal disappears entirely and leaves the inferior alveolar nerve without its bony protection, although it is still covered by soft tissue.

Rarely, a bifid inferior alveolar nerve may be present, in which case a second mandibular foramen, more inferiorly placed, exists and can be detected by noting a doubled mandibular canal on a radiograph (see Chapter 8). Keeping this anatomic variant concerning the mandibular foramen, as well as its usual location, in mind is important when administering an inferior alveolar block (see Chapter 9).

Overhanging the mandibular foramen is a bony spine, the lingula (lin-gu-lah), which serves as an attachment for the sphenomandibular ligament associated with the temporomandibular joint (see Figure 5-5, A). A small groove, the mylohyoid groove, passes anteriorly to and inferiorly from the mandibular foramen. The mylohyoid nerve and blood vessels travel in the mylohyoid groove.

The articulating surface of the condyle can also be seen in this medial view. This is where the mandible articulates with the temporal bone at the temporomandibular joint (see Chapter 5). Inferior to the articular surface of the condyle on the anterior surface of the neck is a triangular depression, the pterygoid fovea (fo-vee-ah), which serves for the attachment of the lateral pterygoid muscle (see Figures 3-52 and 4-23).

First Cervical Vertebra.: The first cervical vertebra or atlas (at-lis) articulates with the skull at the occipital condyles of the occipital bone (Figure 3-62). The atlas has the form of an irregular ring consisting of two lateral masses connected by a short anterior arch and a longer posterior arch (Figure 3-63). This cervical bone lacks a body and a spine.

The lateral masses can be effectively palpated by placing fingers between the two mastoid processes and the angles of the mandible. More medially, the lateral masses present large concave superior articular processes for the corresponding occipital condyles of the skull. The lateral masses also have circular inferior articular processes for articulation with the second cervical vertebra.

Second Cervical Vertebra.: The second cervical vertebra or axis (ak-sis) is characterized by the dens (denz) or odontoid process (Figure 3-64). The dens articulates anteriorly with the anterior arch of the first cervical vertebra (Figure 3-65). The body of the axis is inferior to the dens. The spine of the axis is located posterior to the body. The body and the adjoining transverse process present superior articular processes for an additional articulation with the inferior articulating surfaces of the atlas. The inferior aspect of the axis presents inferior articular processes for articulating with the articular processes of the third cervical vertebra.

A Superior temporal line

B Foramen rotundum

C External acoustic meatus

D Cribriform plate

E Orbital plate

A Retromolar triangle

B Postglenoid process

C Cribriform plate

D Maxillary tuberosity

E Hamular process

A Temporal bone

B Maxillae

C Sphenoid

D Palatine bone

A Coronal suture

B Squamosal suture

C Sagittal suture

D Lambdoidal suture

A Occipital condyles with atlas

B Occipital condyles with axis

C Mandibular fossa with coronoid notch

D Mandibular fossa with coronoid process

A Lingula

B Submandibular fossa

C Genial tubercles

D External oblique line

E Mandibular foramen

A ethmoid.

B frontal bone.

C maxillae.

D palatine bone.

E lacrimal bone.

A Mental spine

B Median palatine suture

C Retromolar triangle

D Hamulus

E Inferior orbital fissure

A Masseter muscle

B Pterygopalatine ganglion

C Posterior superior alveolar artery

D Maxillary division of the fifth cranial nerve

A mandibular notch.

B coronoid notch.

C temporal fossa.

D infratemporal fossa.

A Level of the first cervical vertebra

B Superior and anterior to the thyroid cartilage

C Articulation with the cartilage of the larynx

D Inferior and posterior to the Adam’s apple

A Alveolar process of the maxilla

B Facial wall of the maxillae

C Infratemporal surface of the maxillae

D Lateral wall of the nasal cavity

A Pterygoid process

B Styloid process

C Mastoid process

D Hamulus

A ostia.

B ducts.

C meatus.

D inferior nasal conchae.

E vestibules.

A Maxillary processes of the maxillae and horizontal plates of the palatine bones

B Palatal processes of the maxillae and maxillary plates of the palatine bones

C Horizontal plates of the palatine bones and palatine processes of the maxillae

D Maxillary plates of the palatine bones and horizontal processes of the maxillae

A Fifth cranial nerve

B Seventh cranial nerve

C Ninth cranial nerve

D Tenth cranial nerve

E Eleventh cranial nerve

A Sphenoid

B Ethmoid

C Occipital

D Vomer

E Parietal

A Medial plate of sphenoid bone

B Lateral plate of sphenoid bone

C Perpendicular plate of ethmoid bone

D Cribriform plate of ethmoid bone

A Vomer

B Maxilla

C Sphenoid bone

D Zygomatic bone

E Mandible

A Squamous

B Tympanic

C Petrous

D Mastoid

A Temporal

B Zygomatic

C Sphenoid

D Inferior nasal conchae

A Fossa

B Foramen

C Fissure

D Perforation

A Occipital

B Mandible

C Parietal

D Sphenoid

A Mylohyoid line

B Mental protuberance

C Mandibular symphysis

D External oblique line

A Frontal

B Maxillae

C Sphenoid

D Zygomatic

A Notch

B Process

C Air cells

D Sinus

A Wing

B Notch

C Body

D Angle

A glabella.

B supraorbital ridge.

C supraorbital notch.

D nasion.

A medial, anterior

B lateral, anterior

C medial, posterior

D lateral, posterior

A Occipital bone

B Mandible

C Maxilla

D Frontal bone

E Ethmoid