Ear

External acoustic meatus

• Divisions
  • Lateral third (cartilaginous)
  • Inner two-thirds (bony)
• Runs from outer ear to middle ear (pinna to tympanic membrane) which is about 4cm
• The junction between cartilaginous and bony parts is about 10-12mm from the tragus and is lateral to the plane of emergence of the facial nerve
• 'Tragal pointer': a small cartilaginous extension of the external portion of the acoustic canal, at the junction with the bony canal, is usually found which seems to point to the facial nerve - about 1cm inferior and 1cm medial to its' tip
• The part of the bony meatus running inferiorly is called the tympanic plate, and the tympanomastoid suture line is found where this joins the mastoid process. This is usually 5-10mm immediately lateral to the facial nerve.