Right systemic arch is absent in

Options

A. Mammals
B. Reptiles
C. Amphibians
D. Birds.

Answer

To solve the question "Right systemic arch is absent in", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Right Systemic Arch**: The right systemic arch is a part of the circulatory system in certain vertebrates. It is important to know which groups of animals possess this structure.

2. **Identify the Groups in the Question**: The question lists four groups: mammals, reptiles, amphibians, and birds. We need to analyze each group to determine the presence or absence of the right systemic arch.

3. **Analyze Each Group**:
- **Mammals**: In mammals, the right systemic arch is absent. They only have the left systemic arch.
- **Reptiles**: Reptiles possess both the right and left systemic arches.
- **Amphibians**: Similar to reptiles, amphibians also have both systemic arches.
- **Birds**: Birds have the right systemic arch present.

4. **Conclusion**: Since the question asks where the right systemic arch is absent, the correct answer is mammals.

### Final Answer:
The right systemic arch is absent in **mammals**.

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