Parietal bone | anatomy | balamut.info
The 2 parietal bone plates meet at the sagittal suture. Lambdoid Each parietal bone plate meets the occipital bone plate at the lambdoid suture. If any of the. The temporal bone forms the lower lateral side of the skull (see Figure ). . The lambdoid suture joins the occipital bone to the right and left parietal and. The skull bones are connected by fibrous joints called sutures. the frontal and parietal bones; Lambdoid suture: between the parietal, temporal, and the intermediate radioulnar joint where the radius and ulna meet above the wrist, in the.
In other animals[ edit ] In non-human vertebrates, the parietal bones typically form the rear or central part of the skull rooflying behind the frontal bones. In many non-mammalian tetrapodsthey are bordered to the rear by a pair of postparietal bones that may be solely in the roof of the skull, or slope downwards to contribute to the back of the skull, depending on the species.
In the living tuataraand many fossil species, a small opening, the parietal foramen, lies between the two parietal bones. This opening is the location of a third eye in the midline of the skull, which is much smaller than the two main eyes. This bone is part of the skull roof, which is a set of bones that cover the brain, eyes and nostrils.
The parietal bones make contact with several other bones in the skull. The anterior part of the bone articulates with the frontal bone and the postorbital bone. The posterior part of the bone articulates with the squamosal bone, and less commonly the supraoccipital bone.
The bone-supported neck frills of ceratopsians were formed by extensions of the parietal bone. These frills, which overhang the neck and extend past the rest of the skull is a diagnostic trait of ceratopsians.
The recognizable skull domes present in pachycephalosaurs were formed by the fusion of the frontal and parietal bones and the addition of thick deposits of bone to that unit. Shape of parietal bone. Parietal bone Side view of the skull.
Important landmarks of the temporal bone, as shown in Figure 7. 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. Mandibular fossa—This is the deep, oval-shaped depression located on the external base of the skull, just in front of the external acoustic meatus.
The mandible lower jaw joins with the skull at this site as part of the temporomandibular joint, which allows for movements of the mandible during opening and closing of the mouth.
Articular tubercle—The smooth ridge located immediately anterior to the mandibular fossa.
Parietal bone - Wikipedia
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.
Styloid process—Posterior to the mandibular fossa on the external base of the skull is an elongated, downward bony projection called the styloid process, so named because of its resemblance to a stylus a pen or writing tool. This structure serves as an attachment site for several small muscles and for a ligament that supports the hyoid bone of the neck.
See also Figure 7. Stylomastoid foramen—This small opening is located between the styloid process and mastoid process. This is the point of exit for the cranial nerve that supplies the facial muscles.
Carotid canal—The carotid canal is a zig-zag shaped tunnel that provides passage through the base of the skull for one of the major arteries that supplies the brain.
Its entrance is located on the outside base of the skull, anteromedial to the styloid process and directly anterior to the jugular foramen. The canal then runs anteromedially within the bony base of the skull, and then turns upward to its exit in the floor of the middle cranial cavity, above the foramen lacerum.
Jugular foramen—The opening in the temporal bone directly posterior to the carotid canal. The is the point of exit for the internal jugular vein. The lesser wing of the sphenoid bone separates the anterior and middle cranial fossae. The petrous ridge petrous portion of temporal bone separates the middle and posterior cranial fossae. Frontal Bone The frontal bone is the single bone that forms the forehead. At its anterior midline, between the eyebrows, there is a slight depression called the glabella see Figure 7.
The frontal bone also forms the supraorbital margin of the orbit. Near the middle of this margin, is the supraorbital foramen, the opening that provides passage for a sensory nerve to the forehead.
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.
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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.
These may result in bleeding inside the skull with subsequent injury to the brain. The most common is a linear skull fracture, in which fracture lines radiate from the point of impact.
Other fracture types include a comminuted fracture, in which the bone is broken into several pieces at the point of impact, or a depressed fracture, in which the fractured bone is pushed inward. In a contrecoup counterblow fracture, the bone at the point of impact is not broken, but instead a fracture occurs on the opposite side of the skull.
Fractures of the occipital bone at the base of the skull can occur in this manner, producing a basilar fracture that can damage the artery that passes through the carotid canal. A blow to the lateral side of the head may fracture the bones of the pterion. The pterion is an important clinical landmark because located immediately deep to it on the inside of the skull is a major branch of an artery that supplies the skull and covering layers of the brain.
A strong blow to this region can fracture the bones around the pterion. If the underlying artery is damaged, bleeding can cause the formation of a hematoma collection of blood between the brain and interior of the skull.
As blood accumulates, it will put pressure on the brain. Symptoms associated with a hematoma may not be apparent immediately following the injury, but if untreated, blood accumulation will exert increasing pressure on the brain and can result in death within a few hours.
Anterior View of Skull
External Website 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 Skull The facial bones of the skull form the upper and lower jaws, the nose, nasal cavity and nasal septum, and the orbit. The facial bones include 14 bones, with six paired bones and two unpaired bones. The paired bones are the maxilla, palatine, zygomatic, nasal, lacrimal, and inferior nasal conchae bones. The unpaired bones are the vomer and mandible bones. The curved, inferior margin of the maxillary bone that forms the upper jaw and contains the upper teeth is the alveolar process of the maxilla Figure 7.
Each tooth is anchored into a deep socket called an alveolus. On the anterior maxilla, just below the orbit, is the infraorbital foramen.
This is the point of exit for a sensory nerve that supplies the nose, upper lip, and anterior cheek. On the inferior skull, the palatine process from each maxillary bone can be seen joining together at the midline to form the anterior three-quarters of the hard palate see Figure 7. The hard palate is the bony plate that forms the roof of the mouth and floor of the nasal cavity, separating the oral and nasal cavities. The maxillary bone forms the upper jaw and supports the upper teeth.
Each maxilla also forms the lateral floor of each orbit and the majority of the hard palate. Palatine Bone The palatine bone is one of a pair of irregularly shaped bones that contribute small areas to the lateral walls of the nasal cavity and the medial wall of each orbit.
The largest region of each of the palatine bone is the horizontal plate. The plates from the right and left palatine bones join together at the midline to form the posterior quarter of the hard palate see Figure 7.
Thus, the palatine bones are best seen in an inferior view of the skull and hard palate. Homeostatic Imbalances…Cleft Lip and Cleft Palate 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. Cleft lip is a common developmental defect that affects approximately 1: 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.
A more severe developmental defect is cleft palate, which affects the hard palate. The hard palate is the bony structure that separates the nasal cavity from the oral cavity.
It is formed during embryonic development by the midline fusion palatine and maxilla bones. Cleft palate affects approximately 1: It results from a failure of the two halves of the hard palate to completely come together and fuse at the midline, thus leaving a gap between them.
This gap allows for communication between the nasal and oral cavities. In severe cases, the bony gap continues into the anterior upper jaw where the alveolar processes of the maxilla bones also do not properly join together above the front teeth.
If this occurs, a cleft lip will also be seen. Because of the communication between the oral and nasal cavities, a cleft palate makes it very difficult for an infant to generate the suckling needed for nursing, thus leaving the infant at risk for malnutrition. Surgical repair is required to correct cleft palate defects.
Zygomatic Bone The zygomatic bone is also known as the cheekbone. Each of the paired zygomatic bones forms much of the lateral wall of the orbit and the lateral-inferior margins of the anterior orbital opening see Figure 7. The short temporal process of the zygomatic bone projects posteriorly, where it forms the anterior portion of the zygomatic arch see Figure 7. Nasal Bone The nasal bone is one of two small bones that articulate with each other to form the bony base bridge of the nose.
They also support the cartilages that form the lateral walls of the nose see Figure 7. These are the bones that are damaged when the nose is broken. Lacrimal Bone Each lacrimal bone is a small, rectangular bone that forms the anterioromedial wall of the orbit see Figure 7.
The anterior portion of the lacrimal bone forms a shallow depression called the lacrimal fossa, and extending inferiorly from this is the nasolacrimal canal. The lacrimal fluid tears of the eyewhich serves to maintain the moist surface of the eye, drains at the medial corner of the eye into the nasolacrimal canal. This duct then extends downward to open into the nasal cavity, behind the inferior nasal concha.
In the nasal cavity, the lacrimal fluid normally drains posteriorly, but with an increased flow of tears due to crying or eye irritation, some fluid will also drain anteriorly, thus causing a runny nose.