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 regarding which type of muscle does not exist in animals, we will analyze the different types of muscle tissues found in the animal body.

### Step-by-Step Solution:

1. **Identify the Types of Muscle Tissues**:
- There are three main types of muscle tissues in animals:
- **Skeletal Muscle**: This muscle is striated and under voluntary control. It is associated with the skeletal system and is responsible for locomotion.
- **Smooth Muscle**: This muscle is unstriated and involuntary. It is found in the walls of hollow organs and is responsible for involuntary movements such as peristalsis in the digestive tract.
- **Cardiac Muscle**: This muscle is striated but involuntary. It is found only in the heart and is responsible for pumping blood.

2. **Analyze Each Option**:
- **Option A (Skeletal Muscle)**: This type of muscle is striated and voluntary. It exists in animals.
- **Option B (Smooth Muscle)**: This type of muscle is unstriated and involuntary. It also exists in animals.
- **Option C (Cardiac Muscle)**: This type of muscle is striated and involuntary. It exists in animals as well.
- **Option D (Unstriated and Voluntary Muscle)**: This type of muscle does not exist in animals. All unstriated muscles (smooth muscles) are involuntary.

3. **Conclusion**:
- The only type of muscle that does not exist in animals is the one described in **Option D**: unstriated but voluntary muscle. Therefore, the correct answer is **Option D**.

### Final Answer:
**Option D: Unstriated but voluntary muscle does not exist in animals.**