TEMPORAL BONE ANATOMY

GENERAL CHARACTERISTICS

• Complex cranial bone situated on skull's lateral and basal aspects
• Located adjacent to external ears
• Supports the temporal region
• Contains structures for hearing and balance
• Protects inner ear organs
• Articulates with surrounding cranial bones

STRUCTURAL COMPONENTS

• Irregular bone composed of multiple distinct parts:
  • Squamous part
  • Tympanic part
  • Petromastoid part
    • Petrous portion
    • Mastoid portion

PETROUS PART

General Features

• Pyramid-shaped region
• Contains apex and base
• Three surfaces present
• Three borders present
• Base oriented laterally
• Among the densest bones in body
• Houses inner ear structures

Apex Region

• Articulates with greater wing of sphenoid
• Articulates with basilar portion of occipital bone

Posterior Border and Mastoid Features

• Posterior Border (occipital margin) — articulates with occipital bone
• Mastoid Process — prominent bony projection
  • Located on external surface of posterior region
  • Serves as attachment for cervical muscles
• Mastoid Notch — groove inferior to mastoid process
  • Attachment site for digastric muscle posterior belly
• Occipital Artery Groove — posterior to mastoid notch
  • Accommodates occipital artery during cranial ascent
• Mastoid Foramen — posterior to mastoid process
  • Transmits emissary veins
  • Connects sigmoid sinus to posterior scalp

Inferior Surface and Carotid Canal

• Carotid Canal — significant passageway in petrous region
  • Begins on inferior petrous surface
  • Opens at petrous apex
  • External opening located medial to jugular fossa
  • Internal opening situated at petrous apex
  • Transmits internal carotid artery to cranial cavity
  • Supplies cerebral blood flow

Musculotubal Canal

• Divided by thin bony septum into two semicanals
• Upper Semicanal — transmits tensor tympani muscle
• Lower Semicanal — accommodates auditory tube
  • Also termed Eustachian tube
  • Connects middle ear to nasopharynx
  • Equalizes pressure across tympanic membrane
• Opens into tympanic cavity
• Located anterior to carotid canal external opening

TYMPANIC PART

General Features

• Curved bony plate
• Positioned anterior to mastoid process
• Forms anterior wall of external acoustic meatus
• Forms floor of external acoustic meatus
• Forms partial posterior wall of external acoustic meatus

Developmental Aspects

• Exists as tympanic ring in neonates
• Fuses with squamous part after birth
• Expands to form mature tympanic part

External Acoustic Meatus

• Bony External Acoustic Opening — meatus entrance
• External Acoustic Meatus — oval canal
  • Approximately 1 cm in length
  • Formed by tympanic and squamous parts
• Tympanic Sulcus — groove within tympanic ring
  • Attachment site for tympanic membrane circumference
• Tympanic Notch — superior deficiency in tympanic ring
  • Allows chorda tympani nerve passage

Tympanic Spines and Styloid Process

• Tympanic Spines:
  • Greater Tympanic Spine — anterior ring projection
  • Lesser Tympanic Spine — posterior ring projection
• Styloid Process Sheath
  • Extends posteriorly from carotid canal
  • Encircles styloid process
• Styloid Process — slender bony projection
  • Attachment for lingual muscles
  • Attachment for pharyngeal ligaments

SQUAMOUS PART

General Features

• Thin flat portion
• Located anterosuperiorly
• Contributes to temporal fossa

Surfaces

• Temporal Surface — outer aspect
  • Smooth and convex
  • Provides temporalis muscle attachment
• Cerebral Surface — inner aspect
  • Concave configuration
  • Accommodates temporal lobe of cerebrum
  • Contains grooves for middle meningeal vessels
  • Shows impressions from cerebral gyri

Borders and Margins

• Superior Border (parietal border)
  • Articulates with parietal bone
  • Forms part of squamous suture
• Parietal Notch — angle between parietal border and mastoid superior border
• Sphenoidal Margin — anteroinferior location
  • Articulates with greater sphenoid wing

Zygomatic Process and Related Structures

• Zygomatic Process — arched projection
  • Extends from inferior squamous portion
  • Contributes to zygomatic arch
  • Connects with temporal process of zygomatic bone
• Supramastoid Crest — continues posteriorly from zygomatic process root
• Suprameatal Fovea — small depression
  • Located between external acoustic meatus posterior wall
  • Located between zygomatic process posterior root
• Suprameatal Spine — anatomical landmark near external acoustic meatus

Mandibular Fossa

• Mandibular Fossa — concave depression
  • Located on inferior squamous surface
  • Contributes to temporomandibular joint
  • Articulates with mandibular condyle
• Articular Surface — anterior mandibular fossa portion
  • Contacts mandible directly
• Articular Tubercle — rounded eminence anterior to fossa
  • Prevents excessive posterior mandibular displacement during jaw opening

TEMPORAL BONE FISSURES

• Separate different bone parts
• Allow nerve and vessel passage
• Petrotympanic Fissure
  • Located between mandibular fossa and tympanic part
  • Posterior to petrosquamous fissure
• Petrosquamous Fissure
  • Anterior to petrotympanic fissure
  • Separates petrous from squamous parts
• Tympanosquamous Fissure
  • Continues petrosquamous and petrotympanic fissures laterally
  • Located between tympanic and squamous parts
• Tympanomastoid Fissure
  • Formed by posterior tympanic edge and mastoid part