External acoustic meatus
The external acoustic meatus (also external auditory meatus, external auditory canal or ear canal, latin: meatus acusticus externus) is an air-filled tubular space that extends from the auricle of the external ear into the temporal bone to the tympanic membrane. The external acoustic meatus conducts sound waves to the tympanic membrane.
The external acoustic meatus is a partly cartilaginous and partly bony S-shaped canal, about 2.5 in length with a diameter about 6 mm, leading to the tympanic membrane, which separates the external ear from the middle ear.
The outer or lateral third of the external acoustic canal is the cartilaginous part, while the inner and posterior walls of the canal are fibrous and lie within the temporal bone, forming the bony part. The cartilage of the external acoustic meatus together with the cartilage of the auricle forms a groove that opens superiorly and posteriorly.
The sensory innervation of the external auditory meatus is provided by branches of several cranial nerves. The auriculotemporal branch of the mandibular nerve (CN V3) with the nerve to external acoustic meatus supplies the anterior and superior wall of the canal with sensory innervation. The auricular branch of the vagus nerve (CN X) supplies the posterior and inferior walls of the canal, and the facial nerve (CN VII) may also supply it due to its connection with the vagus nerve.
The superficial temporal artery supplies the anterior part of the external acoustic meatus, while the posterior auricular artery supplies the posterior part of the ear canal.