The vertebrae of birds are characteristically

Options

A. Heterocoelous
B. Acoelous
C. Opisthocoelous
D. Amphicoelous

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the characteristic type of vertebrae found in birds.

2. **Identifying Vertebrae Types**: There are different types of vertebrae configurations in animals, including heteroceles, aceles, opistoceles, and amphiceles.

3. **Defining Heteroceles**: Heteroceles vertebrae have saddle-shaped articular surfaces. This shape allows for a specific range of motion.

4. **Functionality of Heteroceles**: The saddle shape of heteroceles vertebrae allows for extensive lateral (side-to-side) and vertical (up-and-down) flexion. This flexibility is crucial for the bird's ability to move and maintain balance during flight.

5. **Nerve Cord Consideration**: The design of heteroceles vertebrae ensures that the nerve cord is not excessively stretched during movement. This is important for the bird's overall coordination and function.

6. **Conclusion**: Based on the characteristics and functionality of the vertebrae, we conclude that the vertebrae of birds are characteristically heteroceles.

**Final Answer**: The vertebrae of birds are characteristically heteroceles.

---