| Mastoid part of the temporal bone | |
|---|---|
 Side view of head, showing mastoid part of the temporal bone at right | |
 Occipitomastoid suture (Temporal bone is in purple, and the mastoid portion is immediately to the left of the tip of the arrow.) | |
| Details | |
| Identifiers | |
| Latin | pars mastoidea ossis temporalis |
| FMA | 56088 |
| Anatomical terms of bone | |
Themastoid part of the temporal bone is the posterior (back) part of thetemporal bone, one of thebones of theskull. Its rough surface gives attachment to variousmuscles (viatendons) and it hasopenings forblood vessels. From its borders, the mastoid partarticulates with two other bones.
The word "mastoid" is derived from the Greek word for "breast", a reference to the shape of this bone.
Its outer surface is rough and gives attachment to theoccipitalis andposterior auricular muscles. It is perforated by numerousforamina (holes); for example, themastoid foramen is situated near the posterior border and transmits a vein to thetransverse sinus and a small branch of theoccipital artery to thedura 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.
The mastoid process is located posterior and inferior to theear canal, lateral to thestyloid process, and appears as a conical or pyramidal projection. It forms a bony prominence behind and below the ear.[1] It has variable size and form (e.g. it is larger in themale than in thefemale). It is also filled withsinuses, ormastoid cells. The mastoid process serves for the attachment of thesternocleidomastoid, the posterior belly of thedigastric muscle,splenius capitis, andlongissimus capitis. On the medial side of the process is a deep groove, the mastoid notch, for the attachment of thedigastric muscle; medial to this is a shallow furrow, theoccipital groove, which lodges theoccipital artery. Thefacial nerve passes close to the mastoid process.[2]
The inner surface of the mastoid portion presents a deep, curved groove, thesigmoid sulcus, which lodges part of thetransverse sinus; in it may be seen in the opening of themastoid foramen.
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.
Thesuperior border of the mastoid part is broad and serrated, for articulation with the mastoid angle of the parietal.
Theposterior border, also serrated, articulates with the inferior border of the occipital between the lateral angle andjugular process.
Anteriorly, the mastoid portion is fused with the descending process of thesquama above; below, it enters into the formation of theear canal and thetympanic cavity.
A section of the mastoid process shows it to be hollowed out into a number of spaces, themastoid cells, 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 thetympanic antrum 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, thetegmen tympani, which separates it from the middle fossa of thebase of the skull, below by the mastoid process, laterally by the squama just below thetemporal line, and medially by thelateral semicircular canal of theinternal ear, which projects into its cavity. It opens in front into that portion of the tympanic cavity which is known as the attic orepitympanic recess. 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 towardpuberty.
The mastoid process is absent or rudimentary in the neonatal skull. It forms postnatally (starts to develop after 1 year old),[citation needed] as the sternocleidomastoid muscle develops and pulls on the bone. It usually finishes structural development by 2 years old.[3]
Because of the latepostnatal development of the mastoid process, antenatal injuries to the region often recover spontaneously.[3] The largest size is found inSouth Africans and least found in North American Indians.[4]
Rarely, lesions can develop on the mastoid process.[5]
This article incorporates text in thepublic domain frompage 141 of the 20th edition ofGray's Anatomy(1918)
