The petrous part of the

temporal bone The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples, and house the structures of the ears. Th ...

is pyramid-shaped and is wedged in at the base of the

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

between the sphenoid and

occipital bone The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobe ...

s. Directed medially, forward, and a little upward, it presents a base, an apex, three surfaces, and three angles, and houses in its interior, the components of the

inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...

. The petrous portion is among the most basal elements of the skull and forms part of the

endocranium The endocranium in comparative anatomy is a part of the skull base in vertebrates and it represents the basal, inner part of the cranium. The term is also applied to the outer layer of the dura mater in human anatomy. Structure Structurally, t ...

. Petrous comes from the Latin word ''petrosus'', meaning "stone-like, hard". It is one of the densest bones in the body. The petrous bone is important for studies of ancient DNA from skeletal remains, as it tends to contain extremely well-preserved DNA.

Base

The base is fused with the internal surfaces of the

squamous Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...

and mastoid parts.

Apex

The apex, which is rough and uneven, is received into the angular interval between the posterior border of the

great wing The greater wing of the sphenoid bone, or alisphenoid, is a bony process of the sphenoid bone; there is one on each side, extending from the side of the body of the sphenoid and curving upward, laterally, and backward. Structure The greater win ...

of the

sphenoid bone The sphenoid bone is an unpaired bone of the neurocranium. It is situated in the middle of the skull towards the front, in front of the basilar part of occipital bone, basilar part of the occipital bone. The sphenoid bone is one of the seven bones ...

and the basilar part of the

; it presents the anterior or internal opening of the

carotid canal The carotid canal is a passageway in the temporal bone of the skull through which the internal carotid artery enters the middle cranial fossa from the neck. Structure The carotid canal is located within the middle cranial fossa, at the petrou ...

, and forms the postero-lateral boundary of the

foramen lacerum The foramen lacerum ( la, lacerated piercing) is a triangular hole in the base of skull. It is located between the sphenoid bone, the apex of the petrous part of the temporal bone, and the basilar part of the occipital bone. Structure The for ...

Surfaces

Anterior surface

The anterior surface forms the posterior part of the

middle cranial fossa The middle cranial fossa, deeper than the anterior cranial fossa, is narrow medially and widens laterally to the sides of the skull. It is separated from the posterior fossa by the clivus and the petrous crest. It is bounded in front by the pos ...

of the base of the skull, and is continuous with the inner surface of the squamous portion, to which it is united by the petrosquamous suture, remains of which are distinct even at a late period of life. It is marked by depressions for the convolutions of the brain, and presents six notable points: # near the center, the arcuate eminence (eminentia arcuata), which indicates the location of the superior semicircular canal. # in front of and a little lateral to this eminence, a depression indicating the position of the

tympanic cavity The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound. Structure On its lateral surface, it abuts the external auditory ...

: Here, the layer of bone that separates the tympanic from the cranial cavity is extremely thin, and is known as the ''tegmen tympani'' # a shallow groove, sometimes double, leading lateralward and backward to an oblique opening, the

hiatus for greater petrosal nerve The hiatus for the greater petrosal nerve is a small hole in the petrous part of the temporal bone which connects the facial canal to the middle cranial fossa. The greater petrosal nerve travels through it to branch from the facial nerve and reac ...

, for the passage of the greater petrosal nerve and for the

petrosal branch of the middle meningeal artery The petrosal branch of middle meningeal artery enters the hiatus for greater petrosal nerve, supplies the facial nerve and anastomoses with the stylomastoid branch of the posterior auricular artery. See also * stylomastoid artery The stylomastoid ...

# lateral to the hiatus, a smaller opening, occasionally seen, for the passage of the

lesser superficial petrosal nerve The lesser petrosal nerve (also known as the small superficial petrosal nerve) is the general visceral efferent (GVE) component of the glossopharyngeal nerve (CN IX), carrying parasympathetic preganglionic fibers from the tympanic plexus to the p ...

# near the apex of the bone, the termination of the

, the wall of which in this situation is deficient in front # above this canal the shallow trigeminal impression for the reception of the

trigeminal ganglion A trigeminal ganglion (or Gasserian ganglion, or semilunar ganglion, or Gasser's ganglion) is the sensory ganglion at the base of each of the two trigeminal nerves (CN V), occupying a cavity ( Meckel's cave) in the dura mater, covering the trige ...

Posterior surface

The posterior surface forms the anterior part of the

posterior cranial fossa The posterior cranial fossa is part of the cranial cavity, located between the foramen magnum and tentorium cerebelli. It contains the brainstem and cerebellum. This is the most inferior of the fossae. It houses the cerebellum, medulla and pons. ...

of the base of the skull, and is continuous with the inner surface of the mastoid portion. Near the center is a large orifice, the internal acoustic opening, the size of which varies considerably; its margins are smooth and rounded, and it leads into the

internal auditory meatus The internal auditory meatus (also meatus acusticus internus, internal acoustic meatus, internal auditory canal, or internal acoustic canal) is a canal within the petrous part of the temporal bone of the skull between the posterior cranial fossa ...

a short canal, about 1 cm. in length, which runs lateralward. It transmits the facial and acoustic nerves and the internal auditory branch of the

basilar artery The basilar artery () is one of the arteries that supplies the brain with oxygen-rich blood. The two vertebral arteries and the basilar artery are known as the vertebral basilar system, which supplies blood to the posterior part of the circle of W ...

. The lateral end of the canal is closed by a vertical plate, which is divided by a horizontal crest, the falciform crest, into two unequal portions. Each portion is further subdivided by a vertical ridge into an anterior and a posterior part. * In the ''portion beneath the falciform crest'' are three sets of foramina; these openings together with this central canal transmit the nerves to the

cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory org ...

. ** one group, just below the posterior part of the crest, situated in the

area cribrosa media Area is the quantity that expresses the extent of a region on the plane or on a curved surface. The area of a plane region or ''plane area'' refers to the area of a shape or planar lamina, while '' surface area'' refers to the area of an op ...

, consists of several small openings for the nerves to the

saccule The saccule is a bed of sensory cells in the inner ear. It translates head movements into neural impulses for the brain to interpret. The saccule detects linear accelerations and head tilts in the vertical plane. When the head moves verticall ...

; ** below and behind this area is the

foramen singulare In the temporal bone, in the portion beneath the falciform crest are three sets of foramina; one group, just below the posterior part of the crest, situated in the area cribrosa media, consists of several small openings for the nerves to the saccul ...

, or opening for the nerve to the

posterior semicircular duct The semicircular canals or semicircular ducts are three semicircular, interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the horizontal, superior and posterior semicircular canals. Structure The ...

; ** in front of and below the first is the tractus spiralis foraminosus, consisting of a number of small spirally arranged openings, which encircle the

canalis centralis cochleæ In anatomy, a canal (or canalis in Latin) is a tubular passage or channel which connects different regions of the body. Examples include: * Cranial Region ** Alveolar canals ** Carotid canal ** Facial canal ** Greater palatine canal ** Incisive c ...

. * The ''portion above the crista falciformis'' presents behind, the area cribrosa superior, pierced by a series of small openings, for the passage of the nerves to the utricle and the superior and lateral semicircular ducts, and, in front, the area facialis, with one large opening, the commencement of the canal for the facial nerve (aquæductus Fallopii). Behind the internal acoustic meatus is a small slit almost hidden by a thin plate of bone, leading to a canal, the aquæductus vestibuli, which transmits the ductus endolymphaticus together with a small artery and vein. Above and between these two openings is an irregular depression that lodges a process of the dura mater and transmits a small vein; in the infant, this depression is represented by a large fossa, the

subarcuate fossa In the temporal bone at the sides of the skull, above and between the aquæductus vestibuli is an irregular depression which lodges a process of the dura mater and transmits a small vein Veins are blood vessels in humans and most other animals ...

, which extends backward as a blind tunnel under the superior semicircular canal. # Falciform crest # Area facialis, with (2’) internal opening of the facial canal # Ridge separating the area facialis from the area cribrosa superior # Area cribrosa superior, with (4’) openings for nerve filaments # Anterior inferior cribriform area, with (5’) the tractus spiralis foraminosus, and (5’’) the canalis centralis of the cochlea. # Ridge separating the tractus spiralis foraminosus from the area cribrosa media # Area cribrosa media, with (7’) orifices for nerves to saccule # Foramen singulare.

Inferior surface

The inferior surface is rough and irregular, and forms part of the exterior of the base of the skull. It presents eleven points for examination: # near the apex is a rough surface, quadrilateral in form, which serves partly for the attachment of the

Levator veli palatini The levator veli palatini () is the elevator muscle of the soft palate in the human body. It is supplied via the pharyngeal plexus. During swallowing, it contracts, elevating the soft palate to help prevent food from entering the nasopharynx. ...

and the cartilaginous portion of the

auditory tube Auditory means of or relating to the process of hearing: * Auditory system, the neurological structures and pathways of sound perception ** Auditory bulla, part of auditory system found in mammals other than primates ** Auditory nerve, also known ...

, and partly for connection with the basilar part of the

through the intervention of some dense fibrous tissue # behind this is the large circular aperture of the

, which ascends at first vertically, and then, making a bend, runs horizontally forward and medially; it transmits into the cranium the internal carotid artery, and the carotid plexus of nerves # medial to the opening for the carotid canal and close to its posterior border, in front of the

jugular fossa The jugular fossa is a deep depression in the inferior part of the temporal bone at the base of the skull. It lodges the bulb of the internal jugular vein. Structure The jugular fossa is located in the temporal bone, posterior to the carotid can ...

, is a triangular depression; at the apex of this is a small opening, the aquæductus cochleæ, which lodges a tubular prolongation of the dura mater establishing a communication between the perilymphatic space and the

subarachnoid space In anatomy, the meninges (, ''singular:'' meninx ( or ), ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in th ...

, and transmits a vein from the cochlea to join the internal jugular # behind these openings is a deep depression, the

, of variable depth and size in different skulls; it lodges the bulb of the

internal jugular vein The internal jugular vein is a paired jugular vein that collects blood from the brain and the superficial parts of the face and neck. This vein runs in the carotid sheath with the common carotid artery and vagus nerve. It begins in the posteri ...

# in the bony ridge dividing the carotid canal from the jugular fossa is the small inferior tympanic canaliculus for the passage of the

tympanic branch The tympanic nerve (Jacobson’s nerve) is a branch of the glossopharyngeal nerve found near the ear. It gives sensation to the middle ear, the Eustachian tube, the parotid gland, and mastoid air cells. It gives parasympathetic to supply to the ...

of the

glossopharyngeal nerve The glossopharyngeal nerve (), also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper Medulla oblongata, medulla, just anterior (closer to the nose) to t ...

# in the lateral part of the jugular fossa is the

mastoid canaliculus In the lateral part of the jugular fossa of the temporal bone is the mastoid canaliculus for the entrance of the auricular branch of the vagus nerve, auricular branch of the vagus nerve. Additional images File:Gray187.png, Base of skull. Inferio ...

for the entrance of the

auricular branch of the vagus nerve The auricular branch of the vagus nerve is often termed the Alderman's nerve or Arnold's nerve. The latter name is an eponym for Friedrich Arnold. The auricular branch of the vagus nerve supplies sensory innervation to the skin of the ear canal, t ...

# behind the jugular fossa is a quadrilateral area, the jugular surface, covered with cartilage in the fresh state, and articulating with the

jugular process The jugular process is a quadrilateral or triangular bony plate projecting lateralward from the posterior half of the occipital condyle; it is a part of the lateral part of the occipital bone. The jugular process is excavated in front by the jugul ...

of the

# extending backward from the carotid canal is the vaginal process, a sheath-like plate of bone, which divides behind into two laminæ; the lateral lamina is continuous with the tympanic part of the bone, the medial with the lateral margin of the jugular surface # between these laminæ is the styloid process, a sharp spine, about 2.5 cm. in length # between the styloid and mastoid processes is the stylomastoid foramen; it is the termination of the

facial canal The facial canal (''canalis nervi facialis''), also known as the Fallopian canal, is a Z-shaped canal running through the temporal bone of the skull. It runs from the internal acoustic meatus to the stylomastoid foramen. It contains the facial ...

, and transmits the

facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of tas ...

and

stylomastoid artery The stylomastoid artery enters the stylomastoid foramen and supplies the tympanic cavity, the tympanic antrum and mastoid cells, and the semicircular canals. It is a branch of the posterior auricular artery, and thus part of the external caroti ...

# situated between the tympanic portion and the mastoid process is the

tympanomastoid fissure The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples, and house the structures of the ears. Th ...

, for the exit of the auricular branch of the

vagus nerve The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right ...

Angles

The superior angle, the longest, is grooved for the

superior petrosal sinus The superior petrosal sinus is one of the dural venous sinuses located beneath the brain. It receives blood from the cavernous sinus and passes backward and laterally to drain into the transverse sinus. The sinus receives superior petrosal veins, ...

, and gives attachment to the

tentorium cerebelli The cerebellar tentorium or tentorium cerebelli (Latin for "tent of the cerebellum") is an extension of the dura mater that separates the cerebellum from the inferior portion of the occipital lobes. Structure The cerebellar tentorium is an arche ...

; at its medial extremity is a notch, in which the

trigeminal nerve In neuroanatomy, the trigeminal nerve ( lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and chewin ...

lies. The posterior angle is intermediate in length between the superior and the anterior. Its medial half is marked by a sulcus, which forms, with a corresponding sulcus on the occipital bone, the channel for the inferior petrosal sinus. Its lateral half presents an excavation — the jugular fossa — which, with the jugular notch on the occipital, forms the jugular foramen; an eminence occasionally projects from the center of the fossa, and divides the foramen into two. The anterior angle is divided into two parts—a lateral joined to the squamous part by a suture (petrosquamous), the remains of which are more or less distinct; a medial, free, which articulates with the spinous process of the sphenoid. At the angle of junction of the petrous and the squamous parts are two canals, one above the other, and separated by a thin plate of bone, the septum canalis musculotubarii; both canals lead into the tympanic cavity. * The upper one (semicanalis m. tensoris tympani) transmits the

tensor tympani The tensor tympani is a muscle within the middle ear, located in the bony canal above the bony part of the auditory tube, and connects to the malleus bone. Its role is to dampen loud sounds, such as those produced from chewing, shouting, or th ...

. * the lower one (semicanalis tubae auditivae) forms the bony part of the auditory tube.

The petrous bone in ancient DNA studies

In ancient DNA studies, scientists extract and sequence DNA from ancient skeletal remains of humans and other species. In many cases the DNA is highly degraded, and contaminated by DNA from soil microbes. In 2015 it was found, surprisingly, that the petrous bone has remarkably well-preserved DNA. A 2017 study comparing DNA from different skeletal sites concluded that "The inner part of petrous bones and the cementum layer in teeth roots are currently recognized as the best substrates for (ancient DNA) research ... Both substrates display significantly higher endogenous DNA content (average of 16.4% and 40.0% for teeth and petrous bones, respectively) than parietal skull bone (average of 2.2%)." Consequently, petrous bones are now the most widely-used skeletal site for the study of ancient DNA.

Additional images

File:Gray187.png, Base of skull. Inferior surface. File:Gray193.png, Base of the skull. Upper surface. File:Gray1028.png, Dissection of the muscles of the palate from behind. File:Temporal bone1.jpg, Temporal bone File:Slide25hhhh.JPG, Petrous part of the temporal File:Slide4pppp.JPG, Petrous part of the temporal

References

{{Authority control Bones of the head and neck