The Temporal Bone
The Temporal Bone
Ch. Venkateswararao MDS P.G 1st yrThe temporal bones are situated at the sides and base of the skull. Each consists of five parts, viz., the squama, the petrous, mastoid, and tympanic parts, and the styloid processArticulations.The temporal articulates with five bones: occipital, parietal, sphenoid, mandible and zygomatic.
Styloid processMastoid processExternal acousticmeatusZygomaticprocess (arch)
Temporal boneOccipitalParietal boneSpheoidboneFrontal boneNasal boneZygomaticMandibleMaxilla
Squamous part2 surfaces: external (temporal),internal (cerebral)2 borders : superior and antero inferior .1 process: zygomatic process1 fossa: mandibular fossa
The squama forms the anterior and upper part of the bone, and is scale-like, thin, and translucent.Surfaces.Its outer surface :: Is smooth and convex; Presents:: 1)Groove for middle temporal vessels:: on its hinder part is a vertical groove for the middle temporal artery. above the opening of external auditory meatus 2)supramastoid crest :: runs backward and upward across its posterior part; it serves for the attachment of the temporal fascia, and limits the origin of the Temporalis muscle.. Projecting from the lower part of the squama is a long, arched process, the zygomatic process. 3)Squamo-mastoid suture::
Lies about 1.25 cm below and behind the supramastoid crest,indicates line of fusion b/w squamous and mastoid parts
4)Suprameatal triangle: a small triangular depression b/w the anterior end of supramastoid crest, and the postero- superior sector of external auditory meatus ..Imp: land mark for mastoid antrum ,in adults lies 1.25cm deep to it 5)Suprameatal spine :: small bony projection at anterior part of suprameatal triangle.The posterior end is connected to the squama by two roots, the anterior and posterior roots. The anterior root, continuous with the lower border, is short but broad and strong; it is directed medial ward and ends in a rounded eminence, the articular tubercle (eminentia articularis).
This tubercle forms the front boundary of the mandibular fossa, and in the fresh state is covered with cartilage
6)Zygomatic process:: A long arched process projecting horizontally, laterally and then directed anteriorly from the lower and anterior part of temporal surface; articulates in front with the temporal process of zygomatic bone .
Possesses:: 2 parts , anterior , posteriorAnterior part : thin and flat: has 2 surfaces: lateral :convex & subcutaneous medial: convex & gives origin to masseter muscle from its lower part. 2 borders:: upper: gives attachement to temporal fascia. lower: arched; gives origin to masseter muscle.
2 ends:: anterior : serrated ; articulates with temporal process of zygomatic bone.. Posterior : continous with posterior part of zygomatic process
b)Posterior part :: thick and triangular ..Presents: 3 borders; base: united with squamous part. anterior: constitues anterior root of process. posterior: constitue posterior root of process ..
2 surfaces: superior : concave and continous with temporal surface. inferior: convex and mostly occupied by inferior surface of the anterior root which forms a thickened bar of bone in front of mandibular fossa .The thickened bar of bone is known as articular tubercle. This articulates with the articular disc of TMJ..7) Squamosal foramen :: very rarely present, just above the anterior root of zygomatic processImp: transmits petrosquamous sinus 11) Mandibular fossa: formed by squamous part & partly by tympanic part
Mandibular fossa :: possesses 2 parts :Anterior (articular): formed by squamous part, smooth, oval, convex, articulates with articular disc of TMJ.. Posterior : ( non articular) : formed by tympanic part ,contains a portion of parotid gland .Presents::Post glenoid tubercle: 3rd root of zygomatic process, seperates articular part with non articular part .Squamo-tympanic fissure :.lies between auricular part of mandibular fossa and tympanic part of bone,a) Petrotympanic fissure:: b/w tegmen tympani and tympanic part, transmits anterior tympanic branch of maxillary artery to middle ear, chordatympani nerve,..b) Petro squamous fissure:: b/w tegmen tympani and squamous part, doesnot transmit any structure..
1. Impressions:: corresponding to convolutions of temporal lobe of cerebral hemisphere which lies in relation with it but separated from it by meninges..2. Grooves: for middle meningeal vessels..3.Petro squamosal suture: present inferiorly, where cerebral surface of squamous unites with petrous part .4. Petro squamosal sulcus : present close to the site of union of cerebral surface of squamous part with petrous part; it lodges petro-squamosal sinus..BORDERS:: Superior & antero inferiorSuperior border unites with the inferior border of parietal bone, forms squamosal suture.Antero inferior border articulates with the greater wing of sphenoidInternal surface::
Mastoid Portion (pars mastoidea).The mastoid portion forms the posterior part of the bone
Thicker then squamous part.Presents: 2 surfaces: external (lateral), internal (medial or cerebral);2 borders: superior & posterior.1 process: mastoid processMastoid process: conical projection from antero inferior part of external surface ; larger in males, Presents:: External surface: continous with external part of main part;Mastoid notch: lies in medial aspect of process, Occipital groove:shallow groove ,lies below the notchMastoid foramen: lies close to the posterior border
Transmits: emissiray vein from sigmoid sinus ,small branch of occipital arteryInternal surface:: concave , forms part of posterior cranial fossa.Sigmoid sulcus:: deep curved groove lodges sigmoid sinus; Borders:: superior: short thick serrated, forms a notch with superior border of squamous part; articulates with postero inferior part of parietal bone( mastoid angle).Posterior border: thick & serrated ,articulates with inferior border of squamous part of occipital bone..
Mastoid air cells:: A number of irregular air spaces are present in mastoid part which can be seen in section. larger air space is known as Mastoid or Tympanic antrum; mastoid air cells are inter communicating and they also communicate with middle ear cavity ( tympanic cavity)
Petrous Portion (pars petrosa [pyramis]).The petrous portion or pyramid is pyramidal and is wedged in at the base of the skull between the sphenoid and occipital. contains organ of hearing.
Parts:: Base: fused with squamous and mastoid parts.Apex: lies b/w greater wing of sphenoid and basillar part of occipital ,perieced by anterior orrifice of carotid canal, forms postero lateral boundary of foramen lacerum.3. surfaces: anterior, posterior, inferior. 3. borders ; anterior, superior , posterior.
Anterior surface: continues with cerebral surface of squamous part, forms floor of middle cranial fossa
Parts:Impressions for sulci and gyri of temporal lobe of cerebral hemisphere. Trigeminal impression: depressed area just behind the apex; lodges trigeminal ganglion. second hollow behind the trigeminal impression but seperated from it by an irregular ridge; forms roof of internal auditory meatus & covers cochleaArcuate eminence : elevation behind the second hollow, caused by superior semicircular canal of internal ear ;
5. Tegmen tympani ::thin plate of bone lying between the squamous part laterally & arcuate eminence & the two hollows mediallyForms the roof of mastoid antrum (tympanic), tympanic cavity(middle ear) & canal for tensor tympani; Lateral part meets with the squamous part of petro-squamosal suture & turns down in front to form the lateral canal for tensor tympani, bony part of auditory tube..(pharyngo-tympanic or eustachian tube or acoustic;Presents:: hiatus for greater petrosal nerve, hiatus for lesser petrosal nerve
Posterior surface:: continues with cerebral surface of mastoid part, forma anterior part of posterior cranial fossaPresents: 1. orifice of internal auditory meatus(acousti.)Gives entrance to motor root of facial nerve.Entrance to labyrinthine arteryExit to sensory root of facial nerveExit to vestibulo- cochlear nerveExit to labyrinthine vein.
Diagram of relationship of nerves in theinternal acoustic meatus.VII =facial nerveNI =nervus intermediusVIIIc =cochlear nerveVIIIvs = superior division ofvestibular nerveVIIIvi = inferior division ofvestibular nerve2. Opening of aqueduct of vestibule :small slit, behind the opening of vestibule ,contains saccus, ducts endolymphatics
3.Subarcuate fossa:: irregular depression above & b/w two openings, lodges a process of dura mater..3.Inferior surface:: forms part of inferior surface of base of skull..Presents:: 1.A quadrilateral rough area near the apex gives attachement to cartilaginous part of auditory tube.Its lower part articulates with basillar part of occipital bone.2. External or lower opening of carotid canal :: Transmits; internal carotid artery, with plexus of sympathetic nerves, internal carotid plexus of veins.
3.Jugular fossa:: depression behind the carotid canal.,lodges superior bulb of IJV4. A Triangular depression lodges the glossopharyngeal nerve..5. Opening of cochlear canaliculus:: present at apex of triangular depression,leads to cochlear canaliculus, lodges aqueduct of cochlea,prolongation of duramater,6. Opening of tympanic canaliculu