In birds, which flight muscle is well-developed ?

Options

A. Atary
B. Biceps
C. Gastrocnemius
D. Pectoralis major

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which flight muscle is well-developed in birds. This indicates that we need to identify the primary muscle responsible for flight in birds.

2. **Identifying Flight Muscles**: Birds have several muscles that contribute to flight. Among the options provided (artery, biceps, gastrocnemius, pectoralis major), we need to focus on the muscles specifically involved in flying.

3. **Evaluating the Options**:
- **Artery**: This is not a muscle; it is a blood vessel.
- **Biceps**: While this muscle is important for movement in many animals, it is not the primary muscle used for flight in birds.
- **Gastrocnemius**: This muscle is primarily involved in leg movement and is not a flight muscle.
- **Pectoralis Major**: This is a large muscle that plays a crucial role in the downstroke of a bird's wings during flight.

4. **Conclusion**: The pectoralis major muscle is well-developed in birds and is essential for their ability to fly. It originates from the breastbone (sternum) and is responsible for the powerful contractions needed for flight.

5. **Final Answer**: The well-developed flight muscle in birds is the **pectoralis major**.

---