What is the space between arachnoid and piameter called ?

Options

A. Supra-arachnoid space
B. Sub-arachnoid space
C. Subdural space
D. Meninges

Explanation

### Step-by-Step Solution:

1. **Understanding the Meninges**: The brain is protected by three layers of membranes known as meninges. These layers are:
- **Dura Mater**: The outermost layer, tough and protective.
- **Arachnoid Mater**: The middle layer, which is web-like in appearance.
- **Pia Mater**: The innermost layer, which is delicate and closely adheres to the surface of the brain.

2. **Identifying the Space**: The question asks for the space located between the arachnoid mater and the pia mater.

3. **Naming the Space**: The space between the arachnoid mater and the pia mater is specifically called the **subarachnoid space**. This space is filled with cerebrospinal fluid (CSF), which helps to cushion the brain and spinal cord.

4. **Conclusion**: Therefore, the answer to the question is that the space between the arachnoid and pia mater is called the **subarachnoid space**.

5. **Final Answer**: The correct option is **B. Subarachnoid space**.