Length of the cailaginous pa of "Eustachian tube"

The external auditory meatus is 4 cm long and conducts sound waves from the auricle to the tympanic membrane. The framework of the anterior and medial two-thirds of the meatus is elastic cailage (measures 25 mm in length), and the posterior and lateral one third is bony, formed by the tympanic plate (measures 12 mm in length). The sensory nerve supply of the lining skin is derived from the auriculotemporal nerve and the auricular branch of the vagus nerve.The lymph drainage is to the superficial parotid, mastoid, and superficial cervical lymph nodes.