Human Anatomy/Osteology/Skull - Wikibooks, open books for an open world
The parietal bones are two bones in the human skull which, when joined together at a fibrous The occipital angle is rounded and corresponds with the point of meeting of the sagittal The mastoid angle is truncated; it articulates with the occipital bone and with the mastoid portion of the temporal, and presents on its inner. where the parietal bones meet the occipital bone posteriorly (on back of head) where a parietal and temporal bone meet on the lateral aspect of the skull (on. Cranial base: Comprised of six bones – the frontal, sphenoid, ethmoid, occipital, parietal and temporal bones. These bones are important as.
Ossification gradually extends in a radial manner from the center toward the margins of the bone; the angles are consequently the parts last formed, and it is here that the fontanelles exist. Occasionally the parietal bone is divided into two parts, upper and lower, by an antero-posterior suture. 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. The lateral margin is formed by the frontal and zygomatic bones, and the inferior margin by the zygomatic bone and the maxilla.
Below the inferior margin, the maxilla presents the infraorbital foramen, which transmits the corresponding nerve and artery fig. The medial margin, less clearly defined, is formed by the maxilla, the lacrimal and frontal bones. The prominence of the cheek is formed by the zygomatic formerly malar bone fig.
It presents two processes, which articulate with the zygomatic processes of the frontal and temporal bones, respectively.
The bony part of the external nose is formed by the nasal bones and the maxillae. Its opening, to which the cartilaginous part of the nose is anchored in the intact state, is the piriform aperture. Through this the nasal cavity can be seen, divided by the nasal septum into right and left portions. The septum is composed of cartilage in front and bone ethmoid and vomer behind fig.
Each lateral wall of the nasal cavity presents three curled bony plates termed conchae formerly turbinates. The upper jaw is composed of the two maxillae. The growth of the maxillae is responsible for the vertical elongation of the face between the ages of six and twelve years. Each maxilla see fig. The body of the maxilla contributes to the lateral wall of the nasal cavity, the floor of the orbit, the front wall of the infratemporal fossa, and the face. About 1 cm below the lower margin of the orbit, the infra-orbital foramen transmits the infra-orbital nerve and artery.
The two maxillae are united at the intermaxillary suture. The lower jaw, or mandible, which carries the lower teeth in its alveolar part, is described later. Lateral aspect of skull figs. The temporal bone comprises squamous, tympanic, styloid, mastoid, and petrous parts fig.
The parietal bone articulates below with the squamous part ofthe temporal bone see fig. From the squamous portion, the zygomatic process or zygoma projects forward to meet the zygomatic bone and form the zygomatic arch, which is readily palpable in vivo. The upper border of the zygomatic arch corresponds to the lower limit of the cerebral hemisphere see fig.
The lower border of the zygomatic arch, which gives origin to the masseter muscle, can be traced backward to the tubercle of the root of the zygoma, behind which the head of the mandible is lodged in the mandibular fossa. The external acoustic meatus, situated behind the head of the mandible, leads toward the middle ear, from which it is separated in the intact state by the tympanic membrane.
The roof and adjacent part of the posterior wall of the meatus are formed by the squamous part of the temporal bone, whereas the other walls are formed by the tympanic part. A small depression, the suprameatal triangle, lies immediately above and behind the meatus. The mastoid antrum, a cavity in the temporal bone, lies about 1 cm medial to the suprameatal triangle. The floor and anterior wall of the meatus are formed by a curved lamina, the tympanic plate.
In children, it is merely a tympanic ring. The styloid process, of variable length fig. The stylohyoid ligament on each side suspends the hyoid bone from the skull. The mastoid is the back portion of the temporal. In the adult, the mastoid part generally contains air spaces, the mastoid air cells, which communicate with the middle ear by way of the mastoid antrum.
The mastoid process, easily felt in vivo, projects downward and gives attachment to muscles fig. The petrous part is placed deeply and is described later. The temporal line, to which the temporal fascia is attached, arches across the frontal and parietal bones see fig. The temporal fossa, in which the temporal muscle is located, is bounded by the temporal line above and the zygomatic arch below.
The floor of the fossa includes portions of the parietal and frontal bones, the greater wing of the sphenoid bone, and the squamous part of the temporal bone. The area where these four bones approach each other is known as the pterion see fig. The pterion overlies the anterior branch of the middle meningeal artery on the internal aspect of the skull, and it corresponds also to the stem of the lateral sulcus of the brain.
The center of the pterion is about 4 cm above the midpoint of the zygomatic arch and nearly the same distance behind the zygomatic process of the frontal bone see fig. The interval between the zygomatic arch and the rest of the skull is traversed by the temporal muscle, which thereby leaves the temporal fossa and enters the infratemporal fossa. The infratemporal fossa, an irregular space behind the maxilla, is limited medially by the lateral pterygoid plate of the sphenoid bone see fig.
Medial to its communication with the temporal fossa, the roof of the infratemporal fossa is formed by the infratemporal surface of the greater wing of the sphenoid bone fig. The infratemporal fossa contains the lower part of the temporalis and the lateral and medial pterygoid muscles; the maxillary artery and its branches and the pterygoid venous plexus; and the mandibular, maxillary, and chorda tympani nerves.
The infratemporal fossa communicates with the orbit table through the inferior orbital fissure, which is continuous behind with the pterygomaxillary fissure. The infratemporal fossa communicates with the pterygopalatine fossa through the pterygomaxillary fissure, which is between the lateral pterygoid plate and the maxilla and which transmits the maxillary artery.
The pterygopalatine fossa, between the pterygoid plates and the palatine bone, is below the apex of the orbit, and it contains the maxillary artery and nerve. It communicates with the nasal cavity through the sphenopalatine foramen table Inferior aspect of skull figs. These four portions, separable at birth, become fused by the age of about six years.
The foramen magnum is located midway between, and on a level with, the mastoid processes. Through it the posterior cranial fossa and contained brain become continuous with the vertebral canal and contained spinal cord. The foramen magnum contains the medulla oblongata, tonsils of the cerebellum, meninges, and the subarachnoid space; the spinal roots of the accessory nerve, meningeal branches C.
The squamous part of the occipital bone continues from the base onto the back of the skull. The external occipital crest, to which the ligamentum nuchae is attached, extends from the foramen magnum to the external occipital protuberance, which is readily palpable in vivo.
Nuchal lines extend laterally and delimit areas of muscular insertion. The lateral parts of the occipital bone present the occipital condyles at the sides of the foramen magnum.
The condyles articulate with the lateral masses of the atlas and, through them, the weight of the head is transmitted to the vertebral column. The hypoglossal canal, which transmits the hypoglossal nerve, lies hidden above the front of each condyle. The jugular process extends laterally from each condyle to the temporal bone, and its concave anterior border is the posterior boundary of the jugular foramen.
The transverse process of the atlas lies immediately below the jugular process and rarely may be fused with it.
Parietal bone | anatomy | 572233.info
The basilar part of the occipital bone joins the sphenoid bone fig. In front of the foramen magnum, the ill-defined pharyngeal tubercle anchors the pharynx.
Goethe first pointed out clearly the resemblance of the occipital bone to a vertebra. The basilar part and foramen magnum represent the body and vertebral foramen, respectively; the squamous part, with its external occipital protuberance and crest, perhaps represents the laminae and spinous process; and the condyles and jugular processes are in series with the articular and transverse processes, respectively.
Temporal Bone see figs.Skull Anatomy - Bones and Structures - Head Anatomy #1
All five divisions of the temporal bone are seen on the lower surface of the base see fig. The temporal bone contains the middle and internal portions of the ear. The zygomatic process extends forward from the squamous part of the temporal bone to form the zygomatic arch.
The tympanic plate is separated from the head of the mandible by a portion of parotid gland. In the mandibular fossa, the tympanic plate is separated from the squamous part of the temporal bone by the squamotympanic fissure see fig. The fissure is thereby divided into petrosquamous and petrotympanic fissures, and the latter allows the exit of the chorda tympani. The styloid process is separated from the mastoid process by the stylomastoid foramen, through which the facial nerve emerges.
The mastoid part is fused medially with the petrous part, from which it is developed. The mastoid process see fig. The petrous part, shaped like a medially directed pyramid, contains the internal ear and contributes to the boundaries of the middle ear.
Laterally, its base is fused with the rest of the temporal bone. The apex of the petrous part of the temporal bone is directed forward and medially between the sphenoid and occipital bones.
The petrous part of the temporal bone presents anterior and posterior surfaces, which are described with the cranial cavity see pp. The jugular foramen is formed by the petrous part of the temporal bone jugular fossa and by the occipital bone jugular notch see fig.
The jugular foramen is related to the carotid canal anteriorly, the styloid process laterally, the transverse process of the atlas posteriorly, and the hypoglossal canal medially. The foramen transmits the internal jugular vein a continuation of the sigmoid sinus and the glossopharyngeal, vagus, and accessory nerves, as well as a tributary inferior petrosal sinus.
The internal jugular is dilated superior bulb at its commencement. The tympanic nerve from cranial nerve 9 and the auricular branch of cranial nerve 10 pierce the skull in or near the jugular fossa. The carotid canal, a tunnel in the petrous part of the temporal bone, transmits the internal carotid artery and its sympathetic plexus to the cranial cavity.
The entrance to the canal lies immediately in front of the jugular foramen.
- Human Anatomy/Osteology/Skull
- Anatomy of the Newborn Skull
- Parietal bone
The canal is close to the internal ear, and the beating of the artery after exertion may be heard as a thundering sound. Further medially, the quadrate area of the petrous part of the temporal bone gives origin to the levator veli palatini. The groove between the petrous part of the temporal bone and the greater wing of the sphenoid bone is occupied in vivo by the cartilaginous part of the auditory tube.
The foramen lacerum is a jagged opening at the junction of the petrous part of the temporal bone and the sphenoid and occipital bones. It is closed by fibrous tissue in vivo and is a part of the prenatal cartilaginous skull rather than a foramen.
The pterygoid canal passes from the anterior margin of the foramen lacerum to the pterygopalatine fossa. The sphenoid bone consists of a body and three pairs of processes or wings: The greater wing and pterygoid process are described here. The infratemporal surface of the greater wing see figs. It is continuous medially with the lateral pterygoid plate, and it presents two openings into the middle cranial fossa. The anterior and larger is the foramen ovale, which transmits the mandibular nerve.
The posterior and smaller is the foramen spinosum in front of a spur named the spine of the sphenoidwhich transmits the middle meningeal vessels and the meningeal branch of the mandibular nerve. Medial to the foramen ovale and foramen spinosum, the sphenoid bone is separated from the petrous part of the temporal bone by a groove for the cartilaginous part of the auditory tube.
The pterygoid process of each side projects downward from the greater wing, behind the maxilla. Each consists of a lateral and a medial plate separated by the pterygoid fossa.
Chapter 42: The skull and hyoid bone
The medial pterygoid plate, to which the auditory tube is anchored, is prolonged as the pterygoid hamulus. Above, the medial plate presents the scaphoid fossa, which gives origin to the tensor veli palatini; the muscle hooks around the hamulus to gain the soft palate. The lateral pterygoid plate gives origin to the lateral and medial pterygoid muscles see figs.
The nasal cavities are continuous with the nasopharynx through the choanae. They are two large openings above the posterior margin of the bony palate and are separated from each other by the back of the nasal septum vomer.
Laterally, each is bounded by the medial pterygoid plate. Above is found an overlapping complex of vomer, palatine, and sphenoid bones see fig. The bony palate i. It is formed by the palatine processes of the maxillae in front and by the horizontal plates of the palatine bones behind see fig. These four processes are united by a cruciform suture see fig.
The bony palate is covered below by mucoperiosteum. Behind the incisors, a depression incisive fossa allows the passage of nasopalatine nerves through incisive canals and foramina. The posterior border of the bony palate, which presents the posterior nasal spine, gives attachment to the soft palate palatine aponeurosis. Posterolaterally, the bony palate allows the passage of palatine nerves and vessels through greater and lesser palatine foramina and canals.
A cleft palate is one in which the right and left halves have failed to meet in the median plane during development. Cranial cavity The cranial cavity lodges the brain and its meninges, cranial nerves, and blood vessels. It is roofed by the skull cap, and its floor is the upper surface of the base of the skull.
The floor of the cranial cavity is divisible into three "steps," known as the anterior, middle, and posterior cranial fossae, separated by two prominent bony ledges on each side: In young persons, portions of the coronal, sagittal, and lambdoid sutures, as well as the emissary parietal foramina, can be seen. Digital impressions corresponding to gyri of the brain may be visible.
A median sagittal groove for the superior sagittal sinus runs backward on the internal surface of the vault. Depressions termed granular pits are found on each side of the groove, and they lodge lateral lacunae and arachnoid granulations. Numerous vascular grooves for the meningeal vessels are present on the internal surface of the vault. Anterior Cranial Fossa fig. The frontal lobes of the brain rest on the ethmoid, frontal, and sphenoid bones.
The crista galli projects up from the ethmoid bone and gives attachment to the falx cerebri. Behind and at each side of the crista galli, the cribriform plate of the ethmoid bone transmits the filaments of the olfactory nerves from the nasal mucosa to the olfactory bulbs, which lie on the plate.
The ethmoid bone articulates behind with the jugum sphenoidale, a part of the sphenoid bone that unites the right and left lesser wings. Laterally, the orbital plate of the frontal bone roofs the orbit and ethmoidal air sinuses and articulates behind with the lesser wing of the sphenoid bones.
The sphenoidal ridge ofthe lesser wing projects into the lateral sulcus of the brain and ends medially in the anterior clinoid process. The floor resembles a butterfly in that a smaller median part is expanded on each side. The body of the sphenoid bone, which is united to the occipital bone posteriorly, supports the hypophysis above.
The features of the cranial fossae seen in a median section are the jugum sphenoidale, limbus sphenoidalis, chiasmatic groove, tuberculum sellae, hypophysial fossa, dorsum sellae, and clivus fig.
The shallow chiasmatic groove is close to but does not lodge the optic chiasma. The optic canal for the optic nerve and ophthalmic artery leads forward and laterally into the orbit.
It is bounded by the body of the sphenoid bone and the two roots of the lesser wing. The sella turcica is the upper surface of the body of the sphenoid bone between and including the tuberculum sellae the posterior limit of the chiasmatic groove and the dorsum sellae, which juts upward and presents a posterior clinoid process on each side.
The seat of the' 'Turkish saddle" is the hypophysial fossa, which lodges the hypophysis pituitary gland and roofs the sphenoidal airsinuses. Laterally, the carotid groove ascends from the foramen lacerum, then runs forward along the side of the body of the sphenoid bone, and finally ascends medial to the anterior clinoid process. The carotid groove contains the internal carotid artery, embedded in the cavernous sinus.
Near each end of the tuberculum sellae a middle clinoid process may be detectable; it is united by a ligament in some cases by bone to the anterior clinoid process caroticoclinoid foramen.
The lateral part of the middle cranial fossa is formed by the greater wing of the sphenoid bone and by the squamous and petrous parts of the temporal bone. It lodges the temporal lobe of the brain. It is limited by the sphenoidal ridge in front and by the petrous ridge behind. These ridges are closely related to venous sinuses sphenoparietal and superior petrosal, respectively. The superior orbital fissure is a slit between the greater and lesser wings of the sphenoid bone.
It transmits the oculomotor, trochlear, and abducent nerves, and the branches of the ophthalmic nerve see fig. The foramen rotundum, immediately below the medial end of the superior orbital fissure, transmits the maxillary nerve to the pterygopalatine fossa. Behind the foramen rotundum, the foramen ovale transmits the mandibular nerve to the infratemporal fossa. Nearby, the foramen spinosum transmits the middle meningeal vessels, a groove for which can be traced laterally and forward.
The superior orbital fissure, foramen rotundum, foramen ovale, and foramen spinosum are arranged in a crescent on the greater wing of the sphenoid bone see fig. Only the last two of these four openings can be seen on the lower surface of the base. The anterior surface of the petrous part of the temporal bone fig. The abducent nerve bends sharply forward across the apex of the petrous part, medial to the trigeminal ganglion.
Lateral to the ganglion, a rounded elevation arcuate eminence indicates the underlying anterior semicircular canal. Nearby, the hiatus for the greater petrosal nerve proceeds toward the foramen lacerum.
The tympanic cavity and mastoid antrum are roofed by the petrous part of the temporal bone, this part being called the tegmen tympani.
The foramen lacerum, occupied by fibrous tissue in vivo, is at the junction of the petrous part and the sphenoid bone. It marks the end of the carotid canal and the beginning of the carotid groove.
The hindbrain cerebellum, pons, and medulla oblongata occupies the posterior cranial fossa, which is formed by the sphenoid, temporal, parietal, and occipital bones see fig. The fossa is limited above by a dural fold, the tentorium cerebelli, which is attached to the petrous ridge and which separates the cerebellum from the occipital lobes of the brain.
Below, the foramen magnum is evident, and, above the margin of its front part, the hypoglossal canal on each side transmits cranial nerve In front of the foramen magnum, the basilar part of the occipital bone ascends to meet the body of the sphenoid bone.
This sloping surface, termed the clivus see fig. Behind the foramen magnum, the internal occipital crest leads up to the internal occipital protuberance, near which the superior sagittal, straight, and transverse sinuses form a confluence see fig.
A groove for the transverse sinus runs laterally on each side and then turns downward as the groove for the sigmoid sinus, which leads medially and forward into the jugular foramen where the sigmoid sinus becomes the internal jugular veinaccompanied by cranial nerves 9, 10, and The cerebellar fossa on each side lies between the transverse and sigmoid grooves and the foramen magnum.
The occipital lobes of the brain lie on the occipital bone above the transverse sinuses. The posterior surface of the petrous part of the temporal bone presents the internal acoustic meatus, which transmits the facial and vestibulocochlear nerves and the labyrinthine vessels. The internal meatus is almost directly medial to in line with the external acoustic meatus. Behind the internal meatus, a slit the aqueduct of the vestibule transmits the endolymphatic duct of the internal ear see fig.