Ribs move outward during respiration with

Options

A. Intercostal muscles
B. Petrohyal muscles
C. Pharyngeal muscles
D. None of these

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks which muscles are responsible for the outward movement of the ribs during respiration.

2. **Identifying the Types of Respiration**: There are two main phases of respiration:
- Inhalation (inspiration): This is the process of taking air into the lungs.
- Exhalation (expiration): This is the process of expelling air from the lungs.

3. **Identifying the Muscles Involved**: The primary muscles involved in respiration are:
- **Diaphragm**: A dome-shaped muscle that separates the thoracic cavity from the abdominal cavity.
- **Intercostal Muscles**: These are the muscles located between the ribs.

4. **Analyzing the Role of Intercostal Muscles**: During inhalation:
- The diaphragm contracts and flattens, increasing the volume of the thoracic cavity.
- The intercostal muscles contract, causing the ribs to move outward and upward. This movement further increases the volume of the thoracic cavity.

5. **Conclusion**: The outward movement of the ribs during respiration is primarily due to the contraction of the intercostal muscles.

6. **Final Answer**: Therefore, the correct answer to the question is **intercostal muscles**.