Which of the following structure is not filled with endolymph ?

Options

A. Utriculus
B. Tympanic cavity
C. Sacculus
D. Semicircular canal

Answer

To determine which structure is not filled with endolymph, we need to analyze the options provided:

1. **Utriculus**: The utriculus (or utricle) is part of the vestibular system in the inner ear and is filled with endolymph.

2. **Tympanic Cavity**: The tympanic cavity, also known as the middle ear, is an air-filled space located within the temporal bone. It is not filled with endolymph; instead, it contains air.

3. **Succulus**: The succulus (or saccule) is another part of the vestibular system and is also filled with endolymph.

4. **Semicircular Canal**: The semicircular canals are part of the inner ear and are filled with endolymph.

From this analysis, we can conclude that the structure that is not filled with endolymph is the **tympanic cavity**.

### Final Answer:
**Tympanic Cavity**

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