The petrous portion of the temporal bone

Temporal bone

The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum.The temporal bone supports that part of the face known as the temple.-Parts:The temporal bone consists of four parts:* Squama temporalis...

 or pyramid is pyramidal and is wedged in at the base of the skull between the sphenoid and occipital bones. Directed medially, forward, and a little upward, it presents for examination a base, an apex, three surfaces, and three angles, and contains, in its interior, the essential parts of the organ of hearing. The petrous portion is among the most basal elements of the skull and forms part of the endocranium

Endocranium

For internal cast of the cranium, see Endocast.The endocranium in comparative anatomy is a part of the skull base in vertebrates and represent the basal, inner part of the cranium. The term is also applied to the outer layer of the dura mater in human anatomy.-Basic structure:Structurally, the...

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Apex

The apex, rough and uneven, is received into the angular interval between the posterior border of the great wing of the sphenoid and the basilar part of the occipital; it presents the anterior or internal orifice of the carotid canal, and forms the postero-lateral boundary of the foramen lacerum.

Anterior surface

The anterior surface forms the posterior part of the middle fossa 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 points for examination:

1. near the center, the arcuate eminence (eminentia arcuata), which indicates the situation of the superior semicircular canal
   Superior semicircular canal
   The superior semicircular canal is a part of the vestibular system and detects rotation of the head around a rostral-caudal axis.-Structure:...
   
   .
2. in front of and a little lateral to this eminence, a depression indicating the position of the tympanic cavity: Here, the layer of bone that separates the tympanic from the cranial cavity is extremely thin, and is known as the tegmen tympani
3. a shallow groove, sometimes double, leading lateralward and backward to an oblique opening, the hiatus of the facial canal, for the passage of the greater superficial petrosal nerve and the petrosal branch of the middle meningeal artery
4. lateral to the hiatus, a smaller opening, occasionally seen, for the passage of the lesser superficial petrosal nerve
5. near the apex of the bone, the termination of the carotid canal
   Carotid canal
   On the interior surface of the temporal bone, behind the rough surface of the apex, is the large circular aperture of the carotid canal, which ascends at first vertically, and then, making a bend, runs horizontally forward and medialward.-Contents:...
   
   , the wall of which in this situation is deficient in front
6. above this canal the shallow trigeminal impression for the reception of the semilunar ganglion.

Posterior surface

The posterior surface forms the front part of the posterior fossa 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 meatus, the size of which varies considerably; its margins are smooth and rounded, and it leads into 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

Basilar artery

In human anatomy, 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 sometimes together called the vertebrobasilar system, which supplies blood to the posterior part of circle of Willis and anastomoses with...

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The lateral end of the canal is closed by a vertical plate, which is divided by a horizontal crest, the crista falciformis, 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 crista falciformis are three sets of foramina; these openings together with this central canal transmit the nerves to the cochlea.
  • 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 saccule
    Saccule
    The saccule is a bed of sensory cells situated in the inner ear. The saccule translates head movements into neural impulses which the brain can interpret. The saccule is sensitive to linear translations of the head, specifically movements up and down...
    
    ;
  • below and behind this area is the foramen singulare
    Foramen singulare
    In the temporal bone, in the portion beneath the crista falciformis 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 saccule; below and behind this area is the foramen...
    
    , or opening for the nerve to the posterior semicircular duct;
  • 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.

• 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 facians, 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

Subarcuate fossa

In the temporal bone, above and between the aquæductus vestibuli is an irregular depression which lodges a process of the dura mater and transmits a small vein and the subarcuate artery a branch of the internal auditory artery, which is an end artery that supplies blood to the inner ear ; in the...

, which extends backward as a blind tunnel under the superior semicircular canal

Superior semicircular canal

The superior semicircular canal is a part of the vestibular system and detects rotation of the head around a rostral-caudal axis.-Structure:...

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1. Crista falciformis
2. Area facialis, with (2’) internal opening of the facial canal
3. Ridge separating the area facialis from the area cribrosa superior
4. Area cribrosa superior, with (4’) openings for nerve filaments
5. Anterior inferior cribriform area, with (5’) the tractus spiralis foraminosus, and (5’’) the canalis centralis of the cochlea.
6. Ridge separating the tractus spiralis foraminosus from the area cribrosa media
7. Area cribrosa media, with (7’) orifices for nerves to saccule
8. 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:

1. near the apex is a rough surface, quadrilateral in form, which serves partly for the attachment of the Levator veli palatini
   Levator veli palatini
   The levator veli palatini is the elevator muscle of the soft palate in the human body. During swallowing, it contracts, elevating the soft palate to help prevent food from entering the nasopharynx...
   
    and the cartilaginous portion of the auditory tube, and partly for connection with the basilar part of the occipital bone
   Occipital bone
   The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself...
   
    through the intervention of some dense fibrous tissue
2. behind this is the large circular aperture of the carotid canal
   Carotid canal
   On the interior surface of the temporal bone, behind the rough surface of the apex, is the large circular aperture of the carotid canal, which ascends at first vertically, and then, making a bend, runs horizontally forward and medialward.-Contents:...
   
   , 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
3. medial to the opening for the carotid canal and close to its posterior border, in front of the jugular fossa
   Jugular fossa
   The jugular fossa is a deep depression in the inferior part of the base of the skull. More specifically, it is located in the temporal bone, posterior to the carotid canal and the aquæductus cochleæ...
   
   , 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
   Subarachnoid space
   In the central nervous system, the subarachnoid cavity is the interval between the arachnoid membrane and pia mater....
   
   , and transmits a vein from the cochlea to join the internal jugular
4. behind these openings is a deep depression, the jugular fossa
   Jugular fossa
   The jugular fossa is a deep depression in the inferior part of the base of the skull. More specifically, it is located in the temporal bone, posterior to the carotid canal and the aquæductus cochleæ...
   
   , of variable depth and size in different skulls; it lodges the bulb of the internal jugular vein
   Internal jugular vein
   The two internal jugular veins collect the blood from the brain, the superficial parts of the face, and the neck.-Path:On both sides and at the base of the brain, the inferior petrosal sinus and the sigmoid sinus join to form the internal jugular vein...
   
   
5. in the bony ridge dividing the carotid canal from the jugular fossa is the small inferior tympanic canaliculus
   Inferior tympanic canaliculus
   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 of the glossopharyngeal nerve....
   
    for the passage of the tympanic branch of the glossopharyngeal nerve
   Glossopharyngeal nerve
   The glossopharyngeal nerve is the ninth of twelve pairs of cranial nerves . It exits the brainstem out from the sides of the upper medulla, just rostral to the vagus nerve...
   
   
6. in the lateral part of the jugular fossa is the mastoid canaliculus
   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....
   
    for the entrance of the auricular branch of the vagus nerve
7. behind the jugular fossa is a quadrilateral area, the jugular surface, covered with cartilage in the fresh state, and articulating with the jugular process
   Jugular process
   In the lateral part of the occipital bone, extending lateralward from the posterior half of the condyle is a quadrilateral plate of bone, the jugular process, excavated in front by the jugular notch, which, in the articulated skull, forms the posterior part of the jugular foramen.It serves as the...
   
    of the occipital bone
   Occipital bone
   The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself...
   
   
8. 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
9. between these laminæ is the styloid process
   Styloid process
   In anatomy, a styloid process , usually serving as points of attachment for muscles, refers to the slender, pointed process of :* temporal bone of the skull - Temporal styloid process...
   
   , a sharp spine, about 2.5 cm. in length
10. between the styloid and mastoid processes is the stylomastoid foramen
    Stylomastoid foramen
    Between the styloid and mastoid processes of the temporal bone is the stylomastoid foramenIt is the termination of the facial canal, and transmits the facial nerve and stylomastoid artery.- Clinical Relevance :...
    
    ; it is the termination of the facial canal
    Facial canal
    The facial canal is a Z-shaped canal running through the temporal bone from the internal acoustic meatus to the stylomastoid foramen. In humans it is approximately 3 centimeters long, which makes it the longest human osseous canal of a nerve...
    
    , and transmits the facial nerve
    Facial nerve
    The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...
    
     and stylomastoid artery
    Stylomastoid artery
    The stylomastoid artery enters the stylomastoid foramen and supplies the tympanic cavity, the tympanic antrum and mastoid cells, and the semicircular canals...
    
    
11. situated between the tympanic portion and the mastoid process is the tympanomastoid fissure, for the exit of the auricular branch
    Auricular branch
    Auricular branch can refer to any one of several different structures having to do with the ear or hearing:*Nerves**The auricular branch of the vagus nerve - "ramus auricularis nervi vagi"...
    
     of the vagus nerve
    Vagus nerve
    The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
    
    .

Angles

The superior angle, the longest, is grooved for the superior petrosal sinus

Superior petrosal sinus

The superior petrosal sinus is a venous structure located beneath the brain. It receives blood from the cavernous sinus and passes backward and laterally to drain into the transverse sinus....

, and gives attachment to the tentorium cerebelli

Tentorium cerebelli

The tentorium cerebelli or cerebellar tentorium is an extension of the dura mater that separates the cerebellum from the inferior portion of the occipital lobes.-Anatomy:...

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

Trigeminal nerve

The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...

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 squama 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 part and the squama are two canals, one above the other, and separated by a thin plate of bone, the septum canalis musculotubarii (processus cochleariformis); both canals lead into the tympanic cavity.

• The upper one (semicanalis m. tensoris tympani) transmits the Tensor tympani.
• the lower one (semicanalis tubae auditivae) forms the bony part of the auditory tube.