Editing Temporal bone (section)

== Structure ==
The temporal bone consists of four parts—the [[squamous part of temporal bone|squamous]], [[mastoid part of the temporal bone|mastoid]], [[petrous part of the temporal bone|petrous]] and [[tympanic part of the temporal bone|tympanic]] parts.<ref>{{cite web|title= SKULL ANATOMY - TEMPORAL BONE |date=28 June 2017|url=http://www.getbodysmart.com/ap/skeletalsystem/skeleton/axial/skull/cranialbones/temporal/tutorial.html}}</ref><ref>[http://www.claripacs.com/a.php?a=an Temporal bone anatomy on CT] 2012-12-22</ref> The squamous part is the largest and most superiorly positioned relative to the rest of the bone. The [[zygomatic process of temporal bone|zygomatic process]] is a long, arched process projecting from the lower region of the squamous part and it articulates with the [[zygomatic bone]]. Posteroinferior to the squamous is the mastoid part. Fused with the squamous and mastoid parts and between the [[sphenoid bone|sphenoid]] and [[occipital bone]]s lies the [[Petrous portion of the temporal bone|petrous part]], which is shaped like a pyramid. The tympanic part is relatively small and lies inferior to the squamous part, anterior to the mastoid part, and superior to the [[temporal styloid process|styloid process]]. The styloid, from the [[Greek language|Greek]] ''stylos'', is a phallic shaped pillar directed inferiorly and anteromedially between the [[parotid gland]] and [[internal jugular vein]].<ref>{{cite book|last1=Chaurasia|first1=BD|title=Human Anatomy Volume 3|date=31 January 2013|publisher=CBS Publishers and Distributors Pvt Ltd|isbn=9788123923321|pages=41–43|edition=Sixth}}</ref> 

=== Borders ===
{{Gallery|File:Occipitomastoid suture.png|[[Occipitomastoid suture]]. It separates [[occipital bone]] and [[mastoid portion]] of temporal bone.
 |File:SchaedelSeitlichSutur3.png|[[Squamosal suture]]. It separates [[parietal bone]] and [[squama temporalis|squama portion]] of temporal bone.
 |File:SchaedelSeitlichSutur10.png|[[Sphenosquamosal suture]]. It separates [[sphenoid bone]] and [[squama temporalis|squama portion]] of temporal bone.
 |File:SchaedelSeitlichSutur4.png|[[Zygomaticotemporal suture]]. It separates [[zygomatic bone]] and [[zygomatic process of temporal bone]].
}}

=== Development ===
The temporal bone is [[ossified]] from eight centers, exclusive of those for the [[internal ear]] and the [[tympanic ossicle]]s: one for the squama including the zygomatic process, one for the tympanic part, four for the petrous and mastoid parts, and two for the styloid process. Just before the end of [[prenatal development]] [Fig. 6] the temporal bone consists of three principal parts:
# The squama is ossified in membrane from a single nucleus, which appears near the root of the zygomatic process about the second month.
# The petromastoid part is developed from four centers, which make their appearance in the cartilaginous ear capsule about the fifth or sixth month. One (proötic) appears in the neighborhood of the eminentia arcuata, spreads in front and above the [[internal auditory meatus]] and extends to the apex of the bone; it forms part of the cochlea, vestibule, superior semicircular canal, and medial wall of the tympanic cavity. A second (opisthotic) appears at the promontory on the medial wall of the tympanic cavity and surrounds the fenestra cochleæ; it forms the floor of the tympanic cavity and vestibule, surrounds the carotid canal, invests the lateral and lower part of the cochlea, and spreads medially below the internal auditory meatus. A third (pterotic) roofs in the tympanic cavity and antrum; while the fourth (epiotic) appears near the posterior semicircular canal and extends to form the [[mastoid process]] (Vrolik).
# The [[tympanic ring]] is an incomplete circle, in the concavity of which is a groove, the tympanic sulcus, for the attachment of the circumference of the [[eardrum]] (tympanic membrane). This ring expands to form the tympanic part, and is ossified in membrane from a single center which appears about the third month. The styloid process is developed from the proximal part of the cartilage of the second branchial or hyoid arch by two centers: one for the proximal part, the tympanohyal, appears before birth; the other, comprising the rest of the process, is named the stylohyal, and does not appear until after birth. The tympanic ring unites with the squama shortly before birth; the petromastoid part and squama join during the first year, and the tympanohyal portion of the styloid process about the same time [Fig. 7, 8]. The stylohyal does not unite with the rest of the bone until after [[puberty]], and in some skulls never at all.

=== Postnatal development ===
Apart from size increase, the chief changes from birth through puberty in the temporal bone are as follows:
# The [[tympanic ring]] extends outward and backward to form the tympanic part. This extension does not, however, take place at an equal rate all around the circumference of the ring, but occurs more at its anterior and posterior portions. As these outgrowths meet, they create a foramen in the floor of the meatus, the foramen of Huschke. This foramen is usually closed about the fifth year, but may persist throughout life.
# The [[mandibular fossa]] is at first extremely shallow, and looks lateral and inferior; it deepens and directs more inferiorly over time. The part of the squama which forms the fossa lies at first below the level of the zygomatic process. As, the base of the skull thickens, this part of the squama is directed horizontal and inwards to contribute to the [[middle cranial fossa]], and its surfaces look upward and downward; the attached portion of the zygomatic process everts and projects like a shelf at a right angle to the squama.
# The mastoid portion is at first flat, with the stylomastoid foramen and rudimentary styloid immediately behind the tympanic ring. With air cell development, the outer part of the mastoid component grows anteroinferiorly to form the mastoid process, with the styloid and stylomastoid foramen now on the under surface. The descent of the foramen is accompanied by a requisite lengthening of the facial canal.
# The downward and forward growth of the mastoid process also pushes forward the tympanic part; as a result, its portion that formed the original floor of the meatus, and contained the [[Foramen tympanicum|foramen of Huschke]], rotates to become the anterior wall.
# The [[subarcuate fossa]] is nearly effaced.

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File:Gray142.png|1. Outer surface of petromastoid part. 2. Outer surface of tympanic ring. 3. Inner surface of squama.
File:Gray143.png| Temporal bone at birth. Outer aspect.
File:Gray144.png| Temporal bone at birth. Inner aspect.
</gallery>