Regulating muscle, which controls the pupil is a part of

Answer

To answer the question regarding which muscle regulates the pupil, we can break down the information step by step.

### Step-by-Step Solution:

1. **Understanding the Eye Structure**:
- The eye consists of various parts including the cornea, iris, and pupil. The pupil is the opening through which light enters the eye.

2. **Identifying the Muscle**:
- The muscle that controls the size of the pupil is known as the **iris muscle**.

3. **Types of Iris Muscles**:
- The iris muscle is composed of two types of muscles:
- **Sphincter muscle**: This muscle contracts to make the pupil smaller, reducing the amount of light that enters the eye.
- **Dilatory muscle**: This muscle relaxes to allow the pupil to expand, increasing the amount of light that can enter the eye.

4. **Function of the Iris Muscles**:
- The action of these muscles is regulated based on the intensity of light:
- In bright light, the sphincter muscle contracts, making the pupil smaller (constriction).
- In dim light, the dilatory muscle contracts, allowing the pupil to expand (dilation).

5. **Conclusion**:
- Therefore, the muscle responsible for regulating the size of the pupil is the **iris muscle**.

### Final Answer:
The regulating muscle that controls the pupil is the **iris muscle**.

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