(i) Part labelled ‘A’ is called as ear ossicles. It is made up of three bones malleus, incus and stapes. These ear ossicles transmit the sound waves from external to the internal ear.
(ii) Part labelled ‘B’ is called as eustachian tube. It acts as ventilator to equalize pressure of air on both the sides of tympanic membrane that forms the outer boundary of middle ear.
(iii) Part labelled ‘C’ is auditory nerve (vestibular and cochlear nerve) which carries hearing impulses to the brain.
(iv) Ear wax lubricates the tympanum for proper functioning.