Final answer:
The choroid is not a structure of the ear but is associated with the eye. The structures of the ear include the cochlea, incus, and stapes, all of which play critical roles in the process of hearing.
Step-by-step explanation:
When considering the structures of the ear, the choroid is not one of them. Instead, the ear primarily consists of the cochlea, the incus, and the stapes. The cochlea is part of the inner ear and is crucial for audition as it transduces sound waves into neural signals. The incus, also known as the anvil, is one of the three ossicles in the middle ear that transmit sound vibrations from the tympanic membrane to the inner ear. Similarly, the stapes or stirrup is another tiny bone in the middle ear assisting in the transmission of sound. However, the choroid is associated with the eye, not the ear, and thus, it is the correct answer to the question about which structure is not part of the ear.