In this article we will discuss about the parts and surfaces of temporal bones which belongs to human skull.
Parts of Temporal Bone:
Paired bones, situated along the lower part of the lateral wall of the cranium. It contains the hearing and vestibular organs and takes part in the formation of temparo mandibular joint.
Parts of Temporal Bone:
It has five parts:
1. Squamous part
2. Petrous part
3. Mastoid part
4. Tympanic part
5. Styloid part.
1. Squamous Part:
It is the upper expanded part, forms lateral wall of the cranium. It has two surfaces – medial and lateral surfaces, two borders – superior and inferior borders, one process, i.e., zygomatic process and a mandibular fossa.
Lateral Surface:
Is smooth and slightly convex, takes part in formation of temporal fossa. This surface is grooved by middle temporal vessels. External auditory meatus is also present. Antero superior to the meatus – a ridge called – supra mastoid crest is seen.
Supra Meatal Triangle:
It is a small depression, lies above the external auditory meatus. In the floor of the triangle, supra meatal spine is situated. Deep to the triangle mastoid antrum lies.
Zygomatic Process:
It is a finger like process passes forwards, above and in front of external auditory meatus. It articulates with the temporal process of zygomatic bone and forms zygomatic arch, which separates temporal and infra temporal fossae.
Tubercle of the Root of Zygoma:
Lies at the junction of anterior and posterior parts of the zygomatic process. It gives attachment to the temporo mandibular ligament.
Articular Tubercle:
This elevation lies along the inferior surface of the posterior part of the zygomatic arch, anterior to the mandibular fossa.
Mandibular Fossa:
Is a shallow depression lies between the squamous and tympanic parts, lies behind the articular tubercle. Anterior part of this fossa articulates with the head of the mandible to form temporo mandibular joint.
Post Glenoid Tubercle:
It is present at the root of the zygomatic process, divides the mandibular fossa into anterior and posterior parts.
Squamo Tympanic Fissure:
Lies in the medial part of the mandibular fossa. It is divided into two parts by tegmen tympani – petro tympanic and petro squamous portions. To the petro tympanic fissure the anterior ligament of malleus is attached and it transmits – chorda tympani nerve and anterior tympanic branch of the maxillary artery to supply middle ear.
Muscles Attached:
1. Temporalis muscle originates from lateral surface of squamous part of temporal bone.
2. Temporal fascia is attached upper border of zygomatic arch and lower border and inner surface of the arch gives origin to masseter muscle.
Inner surface of the squmous part – It is related to the temporal lobe of cerebrum, is slightly concave and grooved by middle meningeal vessels. At the junction of petrous and squamous part – petrosquamous suture is present.
Upper border of squamous part articulates with the lower border of parietal bone at squamosal suture. Anteriorly it articulates with the greater wing of sphenoid bone. Squamous part is thin and translucent near mandibular fossa.
2. Petrous Part:
It is stony hard, i.e., hardest part of the bone in the body, pyramidal in shape, sandwitched between sphenoid and occipital bone. It has a base, apex, three surfaces and three borders.
i. Base- Lies laterally, united with mastoid and squamous part of the bone.
ii. Apex- Is directed antero medially and forms foramen lacerum when it comes in contact with sphenoid and basilar part of occipital bone.
iii. Upper opening of carotid canal lies at the apex of the bone.
Surfaces of Temporal Bones:
These are anterior, posterior and inferior surface.
I. Features of the Anterior Surface:
(a) Trigeminal Impression:
Is a small depression at the apex lodging trigeminal ganglion in its cave.
(b) Arcuate Eminence:
Is an elevation overlying the superior semi-circular canal of the internal ear.
(c) Facial Nerve Canal:
Lies deep to postero lateral aspect of the arculate eminence.
(d) Tegmen Tympani:
Is a thin plate of bone lies lateral to arcuate eminence. It forms roof of the middle ear and mastoid antrum, auditory tube and tensor tympani canal.
(e) Grooves on the Anterior Surface:
They are one for greater petrosal nerve situated laterally.
II. Posterior Surface:
It lies behind the superior border of petrous temporal bone, related to cerebellum. It is flat and triangular forms anterior wall of posterior cranial fossa, related to three dural venous sinuses. Superior petrosal sinus lies above, inferior petrosal sinus lies below and sigmoid sinus lies below and behind.
Features on this surface are:
(a) Internal Auditory Meatus:
Lies in the middle of this surface, transmits facial and auditory nerves with labyrinthine vessels.
(b) Opening of Aqueduct of Vestibule:
Like a vertical slit lies postero inferior to internal auditory meatus, directed medially. It lodges saccus and ductus endo lymphaticus part of internal ear.
(c) Subarcuate Fossa:
Is a shallow depression lies postero superior to internal acoustic meatus, directed laterally overlies the superior semicircular canal. It gives attachment to a process of duramater.
III. Inferior Surface of Petrous Temporal Bone:
It is triangular near the apex it gives origin to levator veli palatini muscle. Behind the apex – cartilaginous part of the auditory tube is attached to it.
(a) Opening of Carotid Canal (Inferior Opening):
Lies just posterior to bony part of the auditory tube. It transmits – internal carotid artery with its sympathetic nerve plexus and venous plexus.
(b) Jugular Fossa:
It is situated posterior to the carotid canal opening, lodge’s superior bulb of internal jugular vein and it forms the floor of the middle ear.
(c) Impression of Glossopharyngeal Ganglion:
Lies medial to carotid canal and anterior to jugular fossa.
(d) Tympanic Canaliculus:
It is situated between the carotid canal and jugular fossa. It transmits tympanic branch of glossopharyngeal nerve (Jacobson’s nerve) to middle ear.
(e) Opening for Mastoid Canaliculus:
Lies in the triangular depression for glossopharyngeal ganglion, it leads to the cochlear canaliculus to lodge aqueduct of cochlear and cochlear vein – drains into subarachnoid space.
Jugular Surface:
It articulates with the jugular process of the occipital bone and forms jugular foramen.
Borders of Petrous Part:
(a) Superior Border:
It is grooved by superior petrosal sinus and separates anterior and posterior surface. It gives attachment to the tentorium cerebelli. The medial end of this border is crossed by the sensory and motor roots of the trigeminal nerve, while tip is crossed by abducent nerve deep to petro clinoid ligament of Gruber (canal of Dorollo).
(b) Posterior Border:
Medially it articulates with the basilar part of the occipital bone and is grooved by inferior petrosal sinus. Lateral part forms jugular foramen.
(c) Anterior Border:
Lies in the floor of middle cranial fossa, it articulates with the greater wing of sphenoid medially and laterally with the squamous part of the temporal bone.
At the petro squamosal suture two canals open into the middle ear. Upper canal is for the tensor tympani muscle and lower canal is for Eustachian tube. Both canals are separated by a septum.
3. Mastoid Part:
It is situated postero inferiorly.
It has:
i. Two surfaces – external and internal surface.
ii. Two borders – superior and posterior border.
iii. Prolongation of the external surface is called mastoid process.
A. External Surface:
It is rough and convex gives insertion to – sternomastoid, splenius capitis and longissimus capitis from above downwards.
a. Mastoid Foramen:
Lies near the occipito mastoid suture. It transmits meningeal branch of maxillary artery and an emissary vein connecting sigmoid sinus and posterior auricular vein.
b. Mastoid Notch:
Is present along the medial surface of mastoid process gives origin to posterior belly of digastric. Groove for occipital artery lies medial to the notch.
B. Internal Surface:
Forms posterior cranial fossa, and is grooved by sigmoid sinus.
a. Superior Border of the Mastoid Part:
It is thick and serrated articulates with the inferior border of the parietal bone at the mastoid angle.
b. Posterior Border:
Thick and serrated articulates with the squamous part of the occipital bone.
Mastoid air cells and mastoid antrum are present in the mastoid part. They communicate with the middle ear through aditus. When air cells are not developed mastoid process is solid and sclerotic.
4. Tympanic Part:
Is present below the squamous part, anterior to the mastoid part and forms squamo tympanic fissure and tympano mastoid suture.
It has two surfaces – anterior and posterior surfaces, three borders – lateral, superior and inferior border.
Inferior Surface:
It forms non-articualar part of the mandibular fossa and lodges glenoid part of parotid gland.
Posterior Surface:
It forms major boundary of external auditory meatus – floor, anterior wall and part of posterior wall.
Tympanic Sulcus or Sulcus of Riveni:
Lies along the medial aspect of external auditory meatus, deficient superiorly and gives attachment to the tympanic membrane.
Superior Border:
Squamo tympanic fissure is present. Tegmen tympani turn downwards and divide it into petro tympanic and petro squamous fissures.
Inferior Border:
Enters the inferior surface of petrous part and forms opening of carotid canal and it ends into an expansion to the styloid process enclosing it forming the sheath.
Lateral Border:
Forms the opening of external auditory meatus and gives attachment to the cartilagenous part of the meatus.
5. Styloid Part or Process:
Is about 2.5 cm long, directed downwards and forwards, from the petrous part of the temporal bone. It develops from second pharyngeal arch.
Muscles Attached:
These are styloglossus, stylohyoid and stylopharyngeus takes origin from it.
Ligament Attached:
These are stylohyoid and stylomandibular ligament.
Muscles and ligaments attached to styloid process together they form – styloid apparatus.
The lateral surface of styloid process is crossed by facial nerve, while medially it is related to carotid sheath with its contents. Posteriorly stylomastoid foramen lies – it transmits – facial nerve and stylomastoid branch of posterior auricular artery.
Ossification:
Squamous and tympanic parts are ossified from membrane – primary centre appear at 8th and 12th week of intra uterine life.
Petrous part, mastoid part and styloid process are ossified from cartilage. About 14 centres appear at 20th week of intra uterine life in petrous and mastoid part and fuses with squamous and styloid part during first year.
Styloid process has two centers – one in the upper part appears just before birth and one for the lower part appears by 2nd year.