## Core Concept
The semicircular canals are part of the **vestibular system** in the inner ear, which is responsible for detecting changes in head position, movement, and acceleration. They are filled with a fluid called **endolymph** and are lined with sensory hair cells.

## Why the Correct Answer is Right
The correct answer, , states that the semicircular canals are **ampullae**. The ampullae are the dilated ends of the semicircular canals and contain sensory hair cells that detect movement of the endolymph. This structure is crucial for the detection of rotational movements of the head.

## Why Each Wrong Option is Incorrect
* **Option A:** This option is incorrect because it does not accurately describe a characteristic specific to semicircular canals.
* **Option B:** This option is incorrect as it does not provide a relevant or accurate description related to semicircular canals.
* **Option D:** This option is incorrect because it does not accurately represent a feature or function of the semicircular canals.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the **semicircular canals are responsible for detecting rotational movements**. Damage to these structures can lead to problems with balance and equilibrium.

## Correct Answer Line
**Correct Answer: C. ampullae**