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Temporal bone

German: Os temporale

1 Definition

The temporal bone, belongs to the bones of the skull. It is one of the most detail-rich bones of the human body.

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2 Overview

The temporal bone accommodates the middle and internal ear, and it contributes to the mandibular joint, whose socket it forms. It consists of 4 parts:

3 Squamous part of the temporal bone

3.1 Surfaces

3.1.1 Facies temporalis

The external surface (facies temporalis) of the squamous part of the temporal bone is smooth and convex. It serves as origin for the eponymous temporal muscle and forms a part of the temporal fossa. In its posterior part, you can recognize a vertically ascending groove which accommodates he medial temporal artery.

There is a prominent bony process originating from the anterior part of the facies temporalis, the zygomatic process of the temporal bone. Its superior edge is thin and sharp and also serves as insertion for the temporal fascia. The inferior edge is thicker and curved - there, the fibers of the masseter muscle have their origin. The lateral surface of the process delimitates with the subcutaneous tissue. Its front end articulates with the temporal process of the zygomatic bone and thus forms the zygomatic arch (arcus zygomaticus). On the posterior end of the zygomatic process, two bone crests create a connection to the squamous part. Here, you also can find the mandibular fossa covered by cartilage. The zygomatic process continues in a flat bone crest in dorsal direction, the supramastoid crest It serves as insertion for the temporal fascia and narrows the origin of the temporal muscle. Around 1 cm below the crest, sometimes recognizable in the remains of a suture, there is the dividing line between the squamous part and the mastoid part.

3.1.2 Facies cerebralis

The internal surface of the squamous part (facies cerebralis) is concave. It shows flat impressions which originate from the temporal lobe of the brain, and bone grooves for the accommodation of the branches of the medial meningeal artery.

3.2 Edges

The superior edge (margo superior) of the temporal bone has a thin end, while the external lamina (tabula externa) overtops the internal lamina (tabula interna). It articulates with the parietal bone in the squamous suture. The anteroinferior edge (margo anteroinferior) is thick and serrated, and it articulates with the greater wing of the sphenoid bone.

4 Tympanic part of the temporal bone

The tympanic part of the temporal bone is a curved bone section caudal to the squamous part. It is located in front of the mastoid process and surrounds the external acoustic meatus. The tympanic part develops as separate bone which merges with the other parts of the temporal bone during cranial growth. In some mammal species, however, it remains as separate bone.

4.1 Surfaces

The posterosuperior surface is concave and shapes the anterior wall, the floor, as well as parts of the posterior wall of the external acoustic meatus. Medially, you can see a small crest where the eardrum inserts, the so-called tympanic crest.

The anteroinferior surface also is slightly concave. It forms the posterior delimitation of the mandibular fossa, and it is in contact with the retromandibular part of the parotid gland.

4.2 Edges

The lateral edge of the tympanic part, where the cartilagineous part of the external acoustic meatus inserts, shows a rough bone surface where again fibers of connective tissue insert.
The posterior edge connects with the squamous and mastoid part, and it shapes the anterior delimitation of the tympanomastoid fissure.
Laterally, the superior edge is in contact with the backside of the postglenoidal process, medially, with the petrotympanic fissure.
The medial part of the inferior edge is thin and terminates sharply. Its lateral part divides to embrace the root of the styloid process as vaginal process. As the stapes, the styloid process and the styloid ligament develop from the 2nd branchial arch, the hyoid arch.

4.3 Other structures

The bony external acoustic meatus is about 2 cm long. It draws towards internal and slightly rostral direction. In sagittal section, an oval, respectively elliptic]] profile appears. The floor, as well as the anterior and the inferior part of the posterior wall, are shaped by the tympanic part. The roof and the superior part of the posterior wall belong to the squamous part.

5 Mastoid part of the temporal bone

5.1 Surfaces

5.1.1 Facies externa

The external surface of the mastoid part is rough and serves as origin of the occipital muscle as well as of the posterior auricular muscle. It is penetrated by numerous foramina. Near the posterior edge of the bone, you can see a larger foramen, the mastoid foramen. A vein to the transverse sinus and a small branch of the occipital artery pass through there. The existence and the location of this foramen can vary. It also can be located in the occipital bone or in the neighboring occipitotemporal suture.

In the inferior part, you can see a marked, conically terminating bone ridge, the mastoid process, which usually is more pronounced in men than in women. Here is the location of the insertion or the origin of different neck muscles, individually the sternocleidomastoideus muscle, the splenius capitis muscle and the posterior venter of the digastric muscle.

On the medial side of the mastoid process, you can see a clear groove, the mastoid notch, the origin of the posterior digastric venter. Immediately medial to it, the occipital artery lies in a small crest (crest of the occipital artery).

5.1.2 Facies interna

On the internal surface of the mastoid part, you can see the sigmoid sulcus, a deep bone groove, which accommodates the sigmoid sinus. The floor of the sulcus is separated from the air cells of the mastoid only by a thin bone lamella.

5.2 Edges

The superior edge of the mastoid part is broad and serrated. It articulates with the mastoid angle of the parietal bone. The posterior edge (margo posterior) articulates with the inferior edge (margo inferior) of the occipital bone between its lateral angle and the jugular process. The anterior edge (margo anterior) is merged with the descending bony process of the squamous part. The inferior edge of the mastoid part forms parts of the external acoustic meatus and the tympanic cavity.

5.3 Spaces

The mastoid part is permeated by numerous air cells, which are called mastoid cells (cellulae mastoideae). Their number, size and expansion vary a lot individually. In the superior and frontal part, they are large and irregularly shaped, and they contain air. Into caudal direction, their size diminishes, so that in the apex, they are only recognizable as small, narrow hollow spaces occasionally containing bone marrow, or they are missing completely.

Additionally, you can find a large hollow space in the anterosuperior region of the mastoid, the tympanic antrum, which is delimited from the mastoid cells as independent anatomical entity, even though it communicates with them via openings in the bone. It also contains air and is coated by the extensions of the mucosa of the tympanic cavity. The tympanic antrum opens to the rostral side into the epitympanic recess of the tympanic cavity. To the upside, it is separated from the middle cranial fossa by a thin bone plate, the tegmen tympani. At the medial wall, the semicircular lateral canal of the internal ear protrudes into the cavity.

6 Petrous part of the temporal bone

see: petrous bone

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Specialties: Anatomy

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