Cranial vault: Bones:Temporal

The temporal bone is situated on the sides and the base of the cranium and lateral to the temporal lobe of cerebrum. The temporal bone is one of the most important calvarial and skull base bones. The temporal bone is very complex and consists of five parts:

* squamous part
* mastoid part
* petrous part
* tympanic part
* styloid process (or part)

The squamous part of the temporal bone (or squamous temporalis/squamous temporal bone) is a very thin bone and forms the anterosuperior aspect of the temporal bone.

#### Gross anatomy

The squamous temporal bone's outer convex surface provides attachment to the temporalis muscle and forms a boundary of the temporal fossa. A curved line, the supramastoid crest (or temporal line), runs posterosuperiorly across its posterior part and provides attachment to the temporalis fascia.

The anterior aspect of the squamous temporal bone extends antero-inferiorly as well as laterally to form the zygomatic process. The superior surface of the zygomatic process provides attachment to the temporalis fascia, whereas its inferior surface is rough and thick surface for the attachment of the masseter muscle.

The posterior root runs above the external auditory meatus and continues with the supramastoid crest. The anterior root is directed medially and ends in the rounded, cartilage-covered, articular eminence, which forms the anterior boundary of the mandibular fossa.

##### Articulations

The squamous temporal bone articulates with various bones include

* superior border articulates with the parietal bone by temporoparietal suture
* anteriorly it articulates with the zygomatic bone through zygomatic process
* anteroinferiorly it articulates with the greater wing of sphenoid bone

The mastoid part of the temporal bone is its posterior component.

#### Gross anatomy

The mastoid part is normally pneumatised by the mastoid air cells and is perforated by the the mastoid foramen.

The mastoid part has an outer rough surface provides attachment to occipitalis and auricularis posterior muscles. It continues inferiorly as the mastoid process, which is a conical bony projection that provides attachment for a number of muscles:

* sternocleidomastoid
* splenius capitis
* the posterior belly of the digastric muscle
* longissimus capitismuscles

On the medial aspect of the mastoid process is a deep groove, called the digastric fossa, where the digastric muscles attach. Medial to this is the he occipital groove, which is traversed by the occipital artery. The sigmoid sulcus, which lodges part of the transverse sinus, lies in the inner surface of the mastoid portion.

##### Articulations

Mastoid part of temporal bone articulates with following bones

* the superior borders articulates with the mastoid angle of the parietal bone
* the posterior border articulates with the inferior border of the occipital bone
* anteriorly it is fused with the descending process of the squamous temporal bone

The petrous part of the temporal bone (or more simply petrous temporal bone) forms the part of skull base between the sphenoid and occipital bones.

#### Gross anatomy

The petrous temporal bone (PTB) has a pyramidal shape with an apex and a base as well as three surfaces and angles:

* apex
	+ direct medially; articulates with posterior aspect of the greater wing of sphenoid and basilar occiput
	+ forms internal border of the carotid canal and the posterolateral boundary of the foramen lacerum
* base
	+ directed laterally and fuses with the internal surface of squama temporalis and mastoid

The PTB has three surfaces - anterior, posterior and inferior:

The anterior surface forms the posterior part of the middle cranial fossa. It is continuous with the inner surface of the squamous part united by the petrosquamous suture. Near its center lies the arcuate eminence, which indicates the location of the superior semicircular canal. Lateral to the arcuate eminence is a depression which indicates the position of middle ear cavity. A shallow groove directed posterolaterally to open into the hiatus of the facial canal. Lateral to this hiatus a smaller hiatus for the lesser petrosal nerve. At the apex the termination of carotid canal is present.

The posterior surface forms the anterior part of posterior cranial fossa. It fuses with the inner surface of mastoid. Near the center of the posterior surface is the internal acoustic meatus. Posteriorly to the internal acoustic meatus is a small slit, leading to the canal of the vestibular aqueduct.

The inferior surface forms part of the exterior of the base of the skull. There are a number of foramina including the inferior opening of the carotid canal and posteriorly the jugular foramen and in between a small inferior tympanic canaliculus, through which the tympanic branch of the glossopharyngeal nerve passes.  The stylomastoid foramen is situated on the inferior surface. It provides attachment to the levator veli palatini and the cartilaginous portion of the auditory tube.

The petrous temporal bone has three angles:

* superior angle:  attachment of tentorium cerebelli, its medial arm lodges the trigeminal nerve and the superior petrosal sinus lodges in the groove of the angle
* posterior angle: contains a sulcus that lodges the inferior petrosal sinus medially and jugular notch of occipital bone forms the jugular foramen laterally
* anterior angle: medial half articulates with the spinous process of the sphenoid and lateral half fuses with the squamous part by the petrosquamous suture

The tympanic part of the temporal bone is situated inferiorly to the squamous part and anteriorly to the mastoid part.

The tympanic part surrounds the external auditory meatus, forming the anterior wall, floor and some posterior wall of the bony external acoustic meatus. The lateral border of tympanic part gives the attachment to the cartilaginous part of the external acoustic meatus. Its anteroinferior surface forms the posterior boundary of the mandibular fossa. It fuses medially with the petrous part and posteriorly with the squamous and mastoid part.

The styloid process (or styloid part of the squamous temporal bone) is a slender pointed part of temporal bone. It projects inferiorly and anteriorly from the inferior surface of the temporal bone, and serves as an anchor point for several muscles associated with the tongue and larynx.

The styloid process provides attachment several muscles associated with the tongue and larynx:

* styloglossus muscle
* stylohyoid muscle
* stylopharyngeus muscle
* stylohyoid ligament
* stylomandibular ligament

It should be noted all of these structures, along with the styloid process, develop from the second branchial arch and form the styloid apparatus.