What provides additional stffness to penis in many mammals ?

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks what provides additional stiffness to the penis in many mammals.

2. **Human Anatomy Context**: In humans, the stiffness of the penis is primarily due to increased blood flow. When a male becomes aroused, blood vessels in the penis dilate, allowing more blood to enter, which causes an erection.

3. **Comparative Anatomy**: However, in many other mammals, particularly certain species like rodents and raccoons, there is a structure known as the baculum, or os penis.

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