Simian gap is

Options

A. Distance between two nostrils
B. Space between incisors and canine
C. Gap between nostrils and upper lip
D. None of the above.

Answer

### Step-by-Step Text Solution:

1. **Understanding the Simian Gap**: The simian gap refers to a specific anatomical feature found in the dentition of apes. It is characterized by a noticeable space or gap between the incisors and canines on each side of the jaw.

2. **Comparison with Human Dentition**: In contrast to apes, humans have a smoothly rounded dental arch that is U-shaped, with small incisors and pointed canines. This difference highlights the evolutionary divergence between humans and apes.

3. **Function of the Simian Shelf**: The simian shelf is a bony thickening located at the front of the ape mandible. Its primary function is to strengthen the jaw. This bony prominence contributes to the simian gap by creating space between the incisors and canines.

4. **Impact on Tongue Movement**: The presence of the simian gap and shelf can also affect the movement of the tongue, as it restricts the area available for the tongue muscles, thereby influencing the range of motion.

5. **Eliminating Incorrect Options**:
- Option 1 states that the simian gap is the distance between the two nostrils, which is incorrect as that space is occupied by the nasal septum.
- Option 3 suggests it is the gap between the nostrils and the upper lip, which is also incorrect; this gap is referred to as the fulcrum.

6. **Conclusion**: Based on the understanding of the simian gap and its anatomical significance, the correct answer is that the simian gap is the space between the incisors and canines in apes.