Identify the ODD term in each set and name the CATEGORY to which the remaining three belong:
Tympanum, Ear ossicles, Auditory canal, Pinna
Topic: Parts of the outer ear
Answer
Odd one out: EAR OSSICLES. Category of the others: PARTS OF THE OUTER (external) EAR.
The PINNA, the AUDITORY CANAL and the TYMPANUM (eardrum) belong to the OUTER ear. The EAR OSSICLES — malleus, incus and stapes — lie in the MIDDLE ear.
So the division is by REGION of the ear, not by function. The three divisions: OUTER — pinna, auditory canal, tympanum MIDDLE — the three ossicles and the Eustachian tube INNER — cochlea, semicircular canals, utriculus, sacculus
Note that the TYMPANUM is conventionally counted with the OUTER ear, as the boundary between outer and middle — which is what makes this question worth asking.