Which is not a vestigial organ in man:

Options

A. Third molar
B. Nails
C. Segmental muscles of abdomen
D. Coccyx

Answer

To determine which organ is not a vestigial organ in humans, we need to understand what vestigial organs are and identify the options provided.

### Step-by-Step Solution:

1. **Understanding Vestigial Organs**:
- Vestigial organs are those that have lost most or all of their original function through the course of evolution. They were functional in our ancestors but are no longer necessary for survival in modern humans.

2. **Identifying the Options**:
- The question presents several options, including:
- A) Third molar (wisdom teeth)
- B) Nails
- C) Segmented muscles of the abdomen
- D) Coccyx (tailbone)

3. **Analyzing Each Option**:
- **Third Molars (Wisdom Teeth)**: These are considered vestigial as they were useful for our ancestors who had a different diet and needed more teeth for grinding food.
- **Nails**: Nails are not vestigial organs. They serve a protective function for the tips of fingers and toes, similar to claws in other animals.
- **Segmented Muscles of the Abdomen**: These muscles are also considered vestigial as they are remnants of muscles that were more functional in our ancestors.
- **Coccyx (Tailbone)**: The coccyx is a vestigial structure that is a remnant of a tail that was present in our ancestors.

4. **Conclusion**:
- From the analysis, it is clear that the only option that is not a vestigial organ is **Nails** (Option B). They serve a protective function and are functional in humans.

### Final Answer:
- The organ that is not a vestigial organ in man is **Nails** (Option B).