Centrum is absent in

Options

A. Atlas vertebra
B. Typical vertebra
C. Sacral vertebra
D. Ninth vertebra.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which vertebra does not have a centrum. The centrum is the central part of a vertebra that provides strength and connects adjacent vertebrae.

2. **Identifying the Options**: The options given are:
- Atlas vertebrae
- Typical vertebrae
- Sexual vertebrae
- 9th vertebrae

3. **Analyzing Each Option**:
- **Atlas Vertebrae**: This is the first cervical vertebra. It is unique because it does not have a centrum. Instead, it has a ring-like structure that supports the skull.
- **Typical Vertebrae**: These vertebrae (like those found in the thoracic and lumbar regions) have a well-defined centrum.
- **Sexual Vertebrae**: This term is not standard in vertebrate anatomy and does not refer to a specific type of vertebra.
- **9th Vertebrae**: This typically refers to a specific vertebra in the thoracic region, which also has a centrum.

4. **Conclusion**: Based on the analysis, the only vertebra that does not have a centrum is the **Atlas vertebrae**.

5. **Final Answer**: The correct option is **Atlas vertebrae**.

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