Mastoid portion of the temporal bone
Encyclopedia
The mastoid portion of the temporal bone
forms the posterior part of the temporal bone.
; it transmits a vein to the transverse sinus and a small branch of the occipital artery
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.
The mastoid portion is continued below into a conical projection, the mastoid process
, the size and form of which vary somewhat; it is larger in the male
than in the female
.
This process serves for the attachment of the Sternocleidomastoid, Splenius capitis, [(the posterior belly of the digastric muscle)], and Longissimus capitis.
On the medial side of the process is a deep groove, the mastoid notch (digastric fossa), for the attachment of the Digastricus; medial to this is a shallow furrow, the occipital groove
, which lodges the occipital artery
.
The inner surface of the mastoid portion presents a deep, curved groove, the sigmoid sulcus
, which lodges part of the transverse sinus; in it may be seen the opening of the mastoid foramen
.
The groove for the transverse sinus is separated from the innermost of the mastoid air cells by a very thin lamina of bone, and even this may be partly deficient.
The posterior border, also serrated, articulates with the inferior border of the occipital between the lateral angle and jugular process
.
Anteriorly the mastoid portion is fused with the descending process of the squama
above; below it enters into the formation of the external acoustic meatus and the tympanic cavity
.
, 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, 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, which separates it from the middle fossa of the base of the skull
; below by the mastoid process; laterally by the squama just below the temporal line
, and medially by the lateral semicircular canal of the internal ear 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 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
.
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...
forms the posterior part of the temporal bone.
Surfaces
Its outer surface is rough, and gives attachment to the Occipitalis and Auricularis posterior. It is perforated by numerous foramina; one of these, of large size, situated near the posterior border, is termed the mastoid foramenMastoid foramen
The mastoid foramen is a large hole in the posterior border of the temporal bone. It transmits a Mastoid emissary vein to the sigmoid sinus and a small branch of the occipital artery, the posterior meningeal artery to the dura mater.-Variations:...
; it transmits a vein to the transverse sinus and a small branch of the occipital artery
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 sterno-mastoid muscles...
to the dura mater
Dura mater
The dura mater , or dura, is the outermost of the three layers of the meninges surrounding the brain and spinal cord. It is derived from Mesoderm. The other two meningeal layers are the pia mater and the arachnoid mater. The dura surrounds the brain and the spinal cord and is responsible for...
.
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 portion is continued below into a conical projection, the mastoid process
Mastoid process
The mastoid process is a conical prominence projecting from the undersurface of the mastoid portion of the temporal bone. It is located just behind the external acoustic meatus, and lateral to the styloid process...
, the size and form of which vary somewhat; it is larger in the male
Male
Male refers to the biological sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilization...
than in the female
Female
Female is the sex of an organism, or a part of an organism, which produces non-mobile ova .- Defining characteristics :The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male...
.
This process serves for the attachment of the Sternocleidomastoid, Splenius capitis, [(the posterior belly of the digastric muscle)], and Longissimus capitis.
On the medial side of the process is a deep groove, the mastoid notch (digastric fossa), for the attachment of the Digastricus; medial to this is a shallow furrow, the occipital groove
Occipital groove
On the medial side of the mastoid process of the temporal bone is a deep groove, the mastoid notch , for the attachment of the Digastricus; medial to this is a shallow furrow, the occipital groove, which lodges the occipital artery....
, which lodges the occipital artery
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 sterno-mastoid muscles...
.
The inner surface of the mastoid portion presents a deep, curved groove, the sigmoid sulcus
Sigmoid sulcus
The inner surface of the mastoid portion of the temporal bone presents a deep, curved groove, the sigmoid sulcus, which lodges part of the transverse sinus; in it may be seen the opening of the mastoid foramen....
, which lodges part of the transverse sinus; in it may be seen the opening of the mastoid foramen
Mastoid foramen
The mastoid foramen is a large hole in the posterior border of the temporal bone. It transmits a Mastoid emissary vein to the sigmoid sinus and a small branch of the occipital artery, the posterior meningeal artery to the dura mater.-Variations:...
.
The groove for the transverse sinus is separated from the innermost of the mastoid air cells by a very thin lamina of bone, and even this may be partly deficient.
Borders
The superior border of the mastoid portion 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
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...
.
Anteriorly the mastoid portion is fused with the descending process of the squama
Squama
Squama refers to a structure shaped like the scale of a fish. More specifically, it can refer to:* Squama frontalis* Squama occipitalis* Squama temporalis, the squamous portion of the temporal bone* Squamous cell...
above; below it enters into the formation of the external acoustic meatus and the tympanic cavity
Tympanic cavity
The tympanic cavity is a small cavity surrounding the bones of the middle ear.It is formed from the tubotympanic recess, an expansion of the first pharyngeal pouch....
.
Spaces
A section of the mastoid process shows it to be hollowed out into a number of spaces, the mastoid cellsMastoid cells
A section of the mastoid process of the temporal bone of the cranium shows it to be hollowed out into a number of spaces, the mastoid cells, which exhibit the greatest possible variety as to their size and number....
, 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, 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, which separates it from the middle fossa of the base of the skull
Base of the skull
The base of skull is the most inferior area of the skull, composed of the endocranium and lower parts of the skull roof.-Bones:*Ethmoid bone*Sphenoid bone*Occipital bone*Frontal bone*Parietal bone*Temporal bone**Petrous portion of the temporal bone...
; below by the mastoid process; laterally by the squama just below the temporal line
Temporal line
Crossing the middle of the parietal bone in an arched direction are two curved lines, the superior and inferior temporal lines; the former gives attachment to the temporal fascia, and the latter indicates the upper limit of the muscular origin of the Temporalis.-External links:*...
, and medially by the lateral semicircular canal of the internal ear 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
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 of the skull. Inflammation which has spread to the...
.
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
Puberty
Puberty is the process of physical changes by which a child's body matures into an adult body capable of reproduction, as initiated by hormonal signals from the brain to the gonads; the ovaries in a girl, the testes in a boy...
.