The mastoid part of the temporal bone is the posterior (back) 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. T ...

, one of the bones of the skull. Its rough surface gives attachment to various muscles (via tendons) and it has openings for blood vessels. From its borders, the mastoid part articulates with two other bones.

Etymology

The word "mastoid" is derived from the Greek word for "

breast The breast is one of two prominences located on the upper ventral region of a primate's torso. Both females and males develop breasts from the same embryological tissues. In females, it serves as the mammary gland, which produces and secret ...

", a reference to the shape of this bone.

Surfaces

Outer surface

Its outer surface is rough and gives attachment to the

occipitalis The occipitalis muscle (occipital belly) is a muscle which covers parts of the skull. Some sources consider the occipital muscle to be a distinct muscle. However, Terminologia Anatomica currently classifies it as part of the occipitofrontalis m ...

and

posterior auricular muscle The posterior auricular muscle is a muscle behind the auricle of the outer ear. It arises from the mastoid part of the temporal bone, and inserts into the lower part of the cranial surface of the auricle of the outer ear. It draws the auricle ba ...

s. It is perforated by numerous

foramina In anatomy and osteology, a foramen (;Entry "foramen"
in

(holes); for example, the

mastoid foramen The mastoid foramen is a hole in the posterior border of the temporal bone. It transmits an emissary vein between the sigmoid sinus and the suboccipital venous plexus, and a small branch of the occipital artery, the posterior meningeal artery t ...

is situated near the posterior border and transmits a vein to the transverse sinus and a small branch of the

occipital artery The occipital artery arises from the external carotid artery opposite the facial artery. Its path is below the posterior belly of digastric to the occipital region. This artery supplies blood to the back of the scalp and sternocleidomastoid musc ...

to the dura mater. The position and size of this foramen are very variable; it is not always present; sometimes it is situated in the occipital bone, or in the suture between the temporal and the occipital.

Mastoid process

The mastoid process is located posterior and inferior to the ear canal, lateral to the styloid process, and appears as a conical or pyramidal projection. It forms a bony prominence behind and below the ear. It has variable size and form (e.g. it is larger in the male than in the female). It is also filled with sinuses, or

mastoid cells The mastoid cells (also called air cells of Lenoir or mastoid cells of Lenoir) are air-filled cavities within the mastoid process of the temporal bone of the cranium. The mastoid cells are a form of skeletal pneumaticity. Infection in these cells ...

. The mastoid process serves for the attachment of the sternocleidomastoid, the posterior belly of the

digastric muscle The digastric muscle (also digastricus) (named ''digastric'' as it has two 'bellies') is a small muscle located under the jaw. The term "digastric muscle" refers to this specific muscle. However, other muscles that have two separate muscle bellie ...

, splenius capitis, and

longissimus capitis The longissimus ( la, the longest one) is the muscle lateral to the semispinalis muscles. It is the longest subdivision of the erector spinae muscles that extends forward into the transverse processes of the posterior cervical vertebrae. Structur ...

. On the medial side of the process is a deep groove, the mastoid notch, for the attachment of the

; medial to this is a shallow furrow, the

occipital groove The mastoid part of the temporal bone is the posterior (back) part of the temporal bone, one of the bones of the skull. Its rough surface gives attachment to various muscles (via tendons) and it has openings for blood vessels. From its borders, t ...

, which lodges the

. The facial nerve passes close to the mastoid process.

Inner surface

The inner surface of the mastoid portion presents a deep, curved groove, the

sigmoid sulcus Sigmoid means resembling the lower-case Greek letter sigma (uppercase Σ, lowercase σ, lowercase in word-final position ς) or the Latin letter S. Specific uses include: * Sigmoid function, a mathematical function * Sigmoid colon, part of the l ...

, which lodges part of the transverse sinus; in it may be seen in the opening of the

. The groove for the transverse sinus is separated from the innermost of the mastoid cells by a very thin lamina of bone, and even this may be partly deficient.

Borders

The ''superior border'' of the mastoid part is broad and serrated, for articulation with the mastoid angle of the parietal. The ''posterior border'', also serrated, articulates with the inferior border of the occipital between the lateral angle and

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 jugu ...

. Anteriorly, the mastoid portion is fused with the descending process of the squama above; below, it enters into the formation of the ear canal and the tympanic cavity.

Spaces

A section of the mastoid process shows it to be hollowed out into a number of spaces, the

, which exhibit the greatest possible variety as to their size and number. At the upper and front part of the process, they are large and irregular and contain air, but toward the lower part, they diminish in size, while those at the apex of the process are frequently quite small and contain marrow; occasionally, they are entirely absent, and the mastoid is then solid throughout. In addition to these a large irregular cavity is situated at the upper and front part of the bone. It is called the

tympanic antrum The mastoid antrum (tympanic antrum, antrum mastoideum, Valsalva's antrum) is an air space in the petrous portion of the temporal bone, communicating posteriorly with the mastoid cells and anteriorly with the epitympanic recess of the middle ear ...

and must be distinguished from the mastoid cells, though it communicates with them. Like the mastoid cells, it is filled with air and lined by a prolongation of the mucous membrane of the tympanic cavity, with which it communicates. The tympanic antrum is bounded above by a thin plate of bone, the

tegmen tympani 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 ...

, which separates it from the middle fossa of the

base of the skull The base of skull, also known as the cranial base or the cranial floor, is the most inferior area of the skull. It is composed of the endocranium and the lower parts of the calvaria. Structure Structures found at the base of the skull are for ...

, below by the mastoid process, laterally by the squama just below the

temporal line The parietal bones () are two bones in the skull which, when joined at a fibrous joint, form the sides and roof of the cranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named ...

, and medially by the

lateral semicircular canal 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 ...

of the

internal ear Internal may refer to: *Internality as a concept in behavioural economics *Neijia, internal styles of Chinese martial arts *Neigong or "internal skills", a type of exercise in meditation associated with Daoism *''Internal (album)'' by Safia, 2016 ...

, which projects into its cavity. It opens in front into that portion of the tympanic cavity which is known as the attic or

epitympanic recess The epitympanic recess is a hollow located on the superior/roof aspect of the middle ear. Clinical significance This recess is a possible route of spread of infection to the mastoid air cells located in the mastoid process of the temporal bone o ...

. The tympanic antrum is a cavity of some considerable size at the time of birth; the mastoid air cells may be regarded as diverticula from the antrum and begin to appear at or before birth. By the fifth year, they are well-marked, but their development is not completed until toward puberty.

Development

The mastoid process is absent or rudimentary in the neonatal skull. It forms postnatally (starts to develop after 1 year old), as the sternocleidomastoid muscle develops and pulls on the bone. It usually finishes structural development by 2 years old.

Clinical significance

Mastoid process

Because of the late postnatal development of the mastoid process, antenatal injuries to the region often recover spontaneously. The largest size is found in South Africans and least found in North American Indians. Rarely, lesions can develop on the mastoid process.

References

External links

* * *
Diagram - #5
(sourc
here
* {{Authority control Bones of the head and neck

Etymology

Surfaces

Outer surface

Mastoid process

Inner surface

Borders

Spaces

Development

Clinical significance

Mastoid process

See also

References

External links