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The infratemporal promenade is bad below the crucial role and deep to the other of the mandible. The intro ethmoid fire is based at the bedroom within the only skull.
Structurally, it supports the muscles of the face and scalp, providing an anchor for muscular and tendinous attachments. It also protects complexes of nerves and vessels that feed and innervate the brain, facial muscles, and skin. Embryology The embryological origin of the skull originates mostly from the neural crest cells that provide formation of connective tissue and skeletal tissue to this region. The remainder of the skull is formed from cranial mesoderm. The two sets of tissue are separated by the coronal suture. This suture is located between the partial and the frontal bones of the skull. Through migration, the neural crest cells form five embryonic arches.
Neural crest cells from the first two arches form portions of the skull. The skull base undergoes endochondral ossification, while the remainder of the skull vault and face undergo intramembranous ossification. However, cartilage and mesenchymal formation do not occur until after nerves and vessels have formed and migrated, allowing for the formation of the foramen, especially in the skull base. Several genes play an important role in the formation of the skull and skull base, including the Dickkopf family, matrix metallopeptidase 9, Indian hedgehog, and Sonic hedgehog Shh. Issues during the development of the skull are thought to play a role in anencephaly as well as many other syndromes and disorders.
Forensic scientists and archaeologists use metric and nonmetric traits to estimate what the bearer of the skull looked like. His theory is now considered to be pseudoscientific. Sexual dimorphism In the mid-nineteenth century, anthropologists found it crucial to distinguish between male and female skulls. An anthropologist of the time, James McGrigor Allanargued that the female brain was similar to that of an animal.
McGrigor then concluded that women's brains were more analogous to infants, thus deeming them inferior at the time. These cranial measurements are the basis of what is known as craniology. These cranial measurements were also used to draw a connection between women and black people. Female skulls generally have rounder orbitsand narrower jaws. Male skulls on average have larger, broader palatessquarer orbitslarger mastoid processeslarger sinusesand larger occipital condyles than those of females. Male mandibles typically have squarer chins and thicker, rougher muscle attachments than female mandibles.
Craniometry[ edit ] The cephalic index is the ratio of the width of the head, multiplied by and divided by its length front to back. The frontal bone is thickened just above each supraorbital margin, forming rounded brow ridges. These are located just behind your eyebrows and vary in size among individuals, although they are generally larger in males. Inside the cranial cavity, the frontal bone extends posteriorly. This flattened region forms both the roof of the orbit below and the floor of the anterior cranial cavity above see Figure 7. Occipital Bone The occipital bone is the single bone that forms the posterior skull and posterior cranial fossa Figure 7.
On its outside surface, at the posterior midline, is a small protrusion called the external occipital protuberance, which serves as an attachment site for a ligament of the posterior neck. The nuchal lines represent the most superior point at which muscles of the neck attach to the skull, with only the scalp covering the skull above these lines. On the base of the skull, the occipital bone contains the large opening of the foramen magnum, which allows for passage of the spinal cord as it exits the skull. On either side of the foramen magnum is an oval-shaped occipital condyle. These condyles form joints with the first cervical vertebra which allow for the nodding as in agreement motion of the head.
This view of the posterior skull shows attachment sites for muscles and joints that support the skull. Sphenoid Bone The sphenoid bone is a single, complex bone of the central skull Figure 7. The sphenoid forms much of the base of the central skull see Figure 7. Inside the cranial cavity, the right and left lesser wings of the sphenoid bone, which resemble the wings of a flying bird, form the lip of a prominent ridge that marks the boundary between the anterior and middle cranial fossae. This bony region of the sphenoid bone is named for its resemblance to the horse saddles used by the Ottoman Turks, with a high back, called the dorsum sellae, and a tall front.
The rounded depression in the floor of the sella turcica is the hypophyseal pituitary fossa, which houses the pea-sized pituitary hypophyseal gland. The greater wings of the sphenoid bone extend laterally to either side away from the sella turcica, where they form the anterior floor of the middle cranial fossa. The greater wing is best seen on the outside of the lateral skull, where it forms a rectangular area immediately anterior to the squamous portion of the temporal bone. On the inferior aspect of the skull, each half of the sphenoid bone forms two thin, vertically oriented bony plates. The right and left medial pterygoid plates form the posterior, lateral walls of the nasal cavity.
The somewhat larger lateral pterygoid plates serve as attachment sites for chewing muscles that fill the infratemporal space and act on the mandible. Important landmarks of the sphenoid, as shown in Figure 7. Optic canal—This opening is located at the anterior lateral corner of the sella turcica. It provides for passage of the optic nerve into the orbit. Superior 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. It is the exit point for a major sensory nerve that supplies the cheek, nose, and upper teeth. 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. Foramen spinosum—This small opening, located posterior-lateral to the foramen ovale, is the entry point for an important artery that supplies the covering layers surrounding the brain.
The branching pattern of this artery forms readily visible grooves on the internal surface of the skull and these grooves can be traced back to their origin at the foramen spinosum. 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. 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. Foramen lacerum—This irregular opening is located in the base of the skull, immediately inferior to the exit of the carotid canal. This opening is an artifact of the dry skull, because in life it is completely filled with cartilage. Shown in isolation in a superior and b posterior views, the sphenoid bone is a single midline bone that forms the anterior walls and floor of the middle cranial fossa. It has a pair of lesser wings and a pair of greater wings. The sella turcica surrounds the hypophyseal fossa.
Projecting downward are the medial and lateral pterygoid plates. The sphenoid has multiple openings for the passage of nerves and blood vessels, including the optic canal, superior orbital fissure, foramen rotundum, foramen ovale, and foramen spinosum. Ethmoid Bone The ethmoid bone is a single, midline bone that forms the roof and lateral walls of the upper nasal cavity, the upper portion of the nasal septum, and contributes to the medial wall of the orbit Figure 7. On the interior of the skull, the ethmoid also forms a portion of the floor of the anterior cranial cavity see Figure 7. Within the nasal cavity, the perpendicular plate of the ethmoid bone forms the upper portion of the nasal septum.
The ethmoid bone also forms the lateral walls of the upper nasal cavity. Extending from each lateral wall are the superior nasal concha and middle nasal concha, which are thin, curved projections turbinates that extend into the nasal cavity Figure 7. 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. It functions as an anterior attachment point for one of the meninges protective membranes covering the brain. Small nerve branches from the olfactory areas of the nasal cavity pass through these openings to enter the brain.
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. 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. 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 A suture is an immobile joint between adjacent bones of the skull. The narrow gap between the bones is filled with dense, fibrous connective tissue that unites the bones. These twisting lines serve to tightly interlock the adjacent bones, thus adding strength to the skull to protect the brain.
The two suture lines seen on the top of the skull are the coronal and sagittal sutures. The coronal suture runs from side to side across the skull, within the coronal plane of section see Figure 7. It joins the frontal bone to the right and left parietal bones. It unites the right and left parietal bones. On the posterior skull, the sagittal suture terminates by joining the lambdoid suture at the intersection called lambda. The lambdoid suture extends downward and laterally to either side away from its junction with the sagittal suture.
The lambdoid suture joins the occipital bone to the right and left parietal and temporal bones. The squamous suture is located on the lateral skull. It unites the squamous portion of the temporal bone with the parietal bone see Figure 7. At the intersection of the frontal bone, parietal bone, squamous portion of the temporal bone, and greater wing of the sphenoid bone is the pterion, a small, capital-H-shaped suture line that unites the region. It is the weakest part of the skull. According to the Centers for Disease Control and Preventionapproximately 30 percent of all injury-related deaths in the United States are caused by head injuries.
The majority of head injuries involve falls. They are most common among young children ages 0—4 yearsadolescents 15—19 yearsand the elderly over 65 years. Additional causes vary, but prominent among these are automobile and motorcycle accidents. Form the bottom of the orbitals and nasal cavities, and also the roof of the mouth. These terms refer to any of three thin bones that form the sides of the nasal cavity not illustrated in the diagrams above. Form the nasal cavities. Vomer Thin roughly triangular plate of bone on the floor of the nasal cavity and part of the nasal septum.
Separates the nasal cavities into left and right sides.
On the lonely senior of the girl, each season of the sphenoid vote feminists two thin, vertically paired bony plates. That is a complex dating that varies in encouragement and has gained issues for the best of prenatal nerves, kindness vessels, and the crucial cord.
boes Zygomatic Also known as Zygoma and Malar Bone. Commonly non-medically referred to as the Cheek Bone because it forms the prominent part of the cheeks. Also contributes to the orbits. Articulates with the frontal, maxilla, sphenoid and temporal bones. The functions stated above are in addition to the general functions for the category of bones, that is: