Design Toscano Gothic Skull Glass-Topped Pedestal, polyresin, Black, One Size

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Facial (14): vomer, two inferior nasal conchae, two nasal, two maxillae, mandible, two palatine, two zygomatic, two lacrimal

The walls of each orbit include contributions from seven skull bones ( Figure 7.3.15). The frontal bone forms the roof and the zygomatic bone forms the lateral wall and lateral floor. The medial floor is primarily formed by the maxilla, with a small contribution from the palatine bone. The ethmoid bone and lacrimal bone make up much of the medial wall and the sphenoid bone forms the posterior orbit. Carotid canal—This is the zig-zag passageway through which a major artery to the brain enters the skull. The entrance to the carotid canal is located on the inferior aspect of the skull, anteromedial to the styloid process (see Figure 7.3.7 a). From here, the canal runs anteromedially within the bony base of the skull. Just above the foramen lacerum, the carotid canal opens into the middle cranial cavity, near the posterior-lateral base of the sella turcica. Maxillary fracture - associated with high-energy trauma. Fractures affecting of maxillary bones are classified using the Le Fort classification, ranging from 1 to 3. View this animation to see how a blow to the head may produce a contrecoup (counterblow) fracture of the basilar portion of the occipital bone on the base of the skull. Why may a basilar fracture be life threatening? Facial Bones of the SkullSuperior orbital fissure—This large, irregular opening into the posterior orbit is located on the anterior wall of the middle cranial fossa, lateral to the optic canal and under the projecting margin of the lesser wing of the sphenoid bone. Nerves to the eyeball and associated muscles, and sensory nerves to the forehead pass through this opening. The skull is a bony structure that supports the face and forms a protective cavity for the brain. It is comprised of many bones, which are formed by intramembranous ossification, and joined by sutures (fibrous joints).

Mylohyoid line—This bony ridge extends along the inner aspect of the mandibular body (see Figure 7.3.10). The muscle that forms the floor of the oral cavity attaches to the mylohyoid lines on both sides of the mandible. In the cranial cavity, the ethmoid bone forms a small area at the midline in the floor of the anterior cranial fossa. This region also forms the narrow roof of the underlying nasal cavity. This portion of the ethmoid bone consists of two parts, the crista galli and cribriform plates. The crista galli (“rooster’s comb or crest”) is a small upward bony projection located at the midline. It functions as an anterior attachment point for one of the meninges (protective membranes covering the brain). To either side of the crista galli is the cribriform plate (cribrum = “sieve”), a small, flattened area with numerous small openings termed olfactory foramina. Small nerve branches from the olfactory areas of the nasal cavity pass through these openings to enter the brain.During embryonic development, the right and left maxilla bones come together at the midline to form the upper jaw. At the same time, the muscle and skin overlying these bones join together to form the upper lip. Inside the mouth, the palatine processes of the maxilla bones, along with the horizontal plates of the right and left palatine bones, join together to form the hard palate. If an error occurs in these developmental processes, a birth defect of cleft lip or cleft palate may result. Foramen ovale of the middle cranial fossa—This large, oval-shaped opening in the floor of the middle cranial fossa provides passage for a major sensory nerve to the lateral head, cheek, chin, and lower teeth. External acoustic meatus (ear canal)—This is the large opening on the lateral side of the skull that is associated with the ear.

Internal acoustic meatus—This opening is located inside the cranial cavity, on the medial side of the petrous ridge. It connects to the middle and inner ear cavities of the temporal bone. Nasal fracture – the most common facial fracture, due to the prominent position of the nasal bones at the bridge of the nose. There is often significant soft tissue swelling and associated epistaxis. The skull is the skeletal structure of the head that supports the face and protects the brain. It is subdivided into the facial bones and the cranium, or cranial vault ( Figure 7.3.1). The facial bones underlie the facial structures, form the nasal cavity, enclose the eyeballs, and support the teeth of the upper and lower jaws. The rounded cranium surrounds and protects the brain and houses the middle and inner ear structures. The brain is almost entirely enclosed by the neurocranium with the exception of the foramen magnum and other foramina at the skull base which serve as entry and exit point for blood vessels and cranial nerves. Also, the skull provides support for all of the facial structures. Key facts Function Fractures of the facial skeleton are relatively common and most frequently result from road traffic collisions, fist fights, and falls.The floor of the brain case is referred to as the base of the skull or cranial floor. This is a complex area that varies in depth and has numerous openings for the passage of cranial nerves, blood vessels, and the spinal cord. Inside the skull, the base is subdivided into three large spaces, called the anterior cranial fossa, middle cranial fossa, and posterior cranial fossa (fossa = “trench or ditch”) ( Figure 7.3.4). From anterior to posterior, the fossae increase in depth. The shape and depth of each fossa correspond to the shape and size of the brain region that each houses. Figure 7.3.4 – Cranial Fossae: The bones of the brain case surround and protect the brain, which occupies the cranial cavity. The base of the brain case, which forms the floor of cranial cavity, is subdivided into the shallow anterior cranial fossa, the middle cranial fossa, and the deep posterior cranial fossa. The paranasal sinuses are named for the skull bone that each occupies. The frontal sinus is located just above the eyebrows, within the frontal bone (see Figure 7.3.16). This irregular space may be divided at the midline into bilateral spaces, or these may be fused into a single sinus space. The frontal sinus is the most anterior of the paranasal sinuses. The largest sinus is the maxillary sinus. These are paired and located within the right and left maxillary bones, where they occupy the area just below the orbits. The maxillary sinuses are most commonly involved during sinus infections. Because their connection to the nasal cavity is located high on their medial wall, they are difficult to drain. The sphenoid sinus is a single, midline sinus. It is located within the body of the sphenoid bone, just anterior and inferior to the sella turcica, thus making it the most posterior of the paranasal sinuses. The lateral aspects of the ethmoid bone contain multiple small spaces separated by very thin bony walls. Each of these spaces is called an ethmoid air cell. These are located on both sides of the ethmoid bone, between the upper nasal cavity and medial orbit, just behind the superior nasal conchae. Figure 7.3.17 – Paranasal Sinuses: The air-filled paranasal sinuses, each named for the bone in which it is found, drain into the nasal cavity. Hyoid Bone The lateral portions of the ethmoid bone are located between the orbit and upper nasal cavity, and thus form the lateral nasal cavity wall and a portion of the medial orbit wall. Located inside this portion of the ethmoid bone are several small, air-filled spaces that are part of the paranasal sinus system of the skull. Figure 7.3.10 – Ethmoid Bone: The unpaired ethmoid bone is located at the midline within the central skull. It has an upward projection, the crista galli, and a downward projection, the perpendicular plate, which forms the upper nasal septum. The cribriform plates form both the roof of the nasal cavity and a portion of the anterior cranial fossa floor. The lateral sides of the ethmoid bone form the lateral walls of the upper nasal cavity, part of the medial orbit wall, and give rise to the superior and middle nasal conchae. The ethmoid bone also contains the ethmoid air cells. Figure 7.3.11 – Lateral Wall of Nasal Cavity: The three nasal conchae are curved bones that project from the lateral walls of the nasal cavity. The superior nasal concha and middle nasal concha are parts of the ethmoid bone. The inferior nasal concha is an independent bone of the skull. Sutures of the Skull

Cleft lip is a common developmental defect that affects approximately 1:1000 births, most of which are male. This defect involves a partial or complete failure of the right and left portions of the upper lip to fuse together, leaving a cleft (gap). It consists of 14 bones, which fuse to house the orbits of the eyes, the nasal and oral cavities, and the sinuses. The frontal bone, typically a bone of the calvaria, is sometimes included as part of the facial skeleton. The cranium (also known as the neurocranium) is formed by the superior aspect of the skull. It encloses and protects the brain, meninges, and cerebral vasculature. The parietal bone forms most of the upper and lateral side of the skull (see Figure 7.3.3). These are paired bones, with the right and left parietal bones joining together at the top of the skull forming the sagittal suture. Each parietal bone is also bounded anteriorly by the frontal bone at the coronal suture, inferiorly by the temporal bone at the squamous suture, and posteriorly by the occipital bone at the lambdoid suture. Figure 7.3.5. Superior view of the skull. Temporal BoneImages, from Anatomy & Physiology by OpenStax, are licensed under CC BY except where otherwise noted. The anterior cranial fossa is the shallowest of the three cranial fossae. It extends from the frontal bone anteriorly to the lesser wing of the sphenoid bone posteriorly. It is divided at the midline by the crista galli and cribriform plates of the ethmoid bone. The middle cranial fossa is located in the central skull, and is deeper than the anterior fossa. The middle fossa extends from the lesser wing of the sphenoid bone anteriorly to the petrous ridge posteriorly. It is divided at the midline by the sella turcica. The posterior cranial fossa is the deepest fossa. It extends from the petrous ridge anteriorly to the occipital bone posteriorly. The large foramen magnum is located at the midline of the posterior fossa. Mandibular foramen—This opening is located on the medial side of the ramus of the mandible. The opening leads into a tunnel that runs down the length of the mandibular body. The sensory nerve and blood vessels that supply the lower teeth enter the mandibular foramen and then follow this tunnel. Thus, to numb the lower teeth prior to dental work, the dentist must inject anesthesia into the lateral wall of the oral cavity at a point prior to where this sensory nerve enters the mandibular foramen. Articular tubercle—The smooth ridge located immediately anterior to the mandibular fossa. Both the articular tubercle and mandibular fossa contribute to the temporomandibular joint, the joint that provides for movements between the temporal bone of the skull and the mandible. On the lateral side of the cranium, above the level of the zygomatic arch, is a shallow space called the temporal fossa. Arising from the temporal fossa and passing deep to the zygomatic arch is another muscle that acts on the mandible during chewing, the temporalis. Figure 7.3.3 – Lateral View and Sagittal Section of Skull: (a) Lateral View of Skull. The lateral skull shows the large rounded brain case, zygomatic arch, and the upper and lower jaws. The zygomatic arch is formed jointly by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone. The shallow space above the zygomatic arch is the temporal fossa. (b) Sagittal Section of Skull. This midline view of the sagittally sectioned skull shows the nasal septum. Bones of the Cranium