Which of these muscles don't exist in animals ?

Options

A. Striated in appearance and voluntary in action
B. Unstriated in appearance and involuntary in action
C. Striated in appearance and involuntary in action
D. Unstriated in appearance and voluntary in action.

Answer

To solve the question "Which of these muscles don't exist in animals?", we will analyze each option provided and determine their characteristics and presence in animals.

### Step-by-Step Solution:

1. **Identify the Types of Muscles**:
- We have four options regarding the types of muscles. We need to evaluate each one.

2. **Option A: Striated in Appearance and Voluntary in Action**:
- These are known as **skeletal muscles**.
- They are striated (having light and dark bands) and are under voluntary control.
- **Conclusion**: Skeletal muscles are found in animals.

3. **Option B: Unstriated in Appearance and Involuntary in Action**:
- These are referred to as **smooth muscles** or **visceral muscles**.
- They are unstriated and operate involuntarily, meaning they are not under conscious control.
- **Conclusion**: Smooth muscles are found in animals.

4. **Option C: Striated in Appearance and Involuntary in Action**:
- These are known as **cardiac muscles**.
- They are striated in appearance, similar to skeletal muscles, but are involuntary in action, meaning they operate without conscious control.
- **Conclusion**: Cardiac muscles are found in animals.

5. **Option D: Unstriated in Appearance and Voluntary in Action**:
- This description does not match any known type of muscle.
- There are no muscles that are both unstriated and voluntary.
- **Conclusion**: This type of muscle does not exist in animals.

### Final Answer:
The correct answer is **Option D: Unstriated in appearance and voluntary in action** does not exist in animals.

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