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 can analyze the options provided:

1. **Utricles**: The utricle is part of the vestibular system located in the inner ear and is filled with endolymph.

2. **Tympanic Cavity**: The tympanic cavity, also known as the middle ear, does not contain endolymph. Instead, it is filled with air and contains the ossicles (tiny bones) that transmit sound vibrations.

3. **Saccula**: The saccule is another part of the vestibular system in the inner ear and is filled with endolymph.

4. **Semicircular Canal**: The semicircular canals are also part of the inner ear and are filled with endolymph, playing a crucial role in balance.

Based on this analysis, the structure that is not filled with endolymph is the **Tympanic Cavity**.

### Step-by-Step Solution:
1. Identify the structures listed in the options: Utricles, Tympanic Cavity, Saccula, Semicircular Canal.
2. Classify these structures based on their location in the ear:
- Utricles, Saccula, and Semicircular Canal are part of the inner ear.
- Tympanic Cavity is part of the middle ear.
3. Determine which of these structures contain endolymph:
- Utricles: Yes, filled with endolymph.
- Tympanic Cavity: No, filled with air.
- Saccula: Yes, filled with endolymph.
- Semicircular Canal: Yes, filled with endolymph.
4. Conclude that the structure that is not filled with endolymph is the **Tympanic Cavity**.