Hollow cavity of diaphysis is  

Options

A. endosteum
B. periosteum
C. both 1 & 2
D. marrow cavity

Answer

To answer the question "Hollow cavity of diaphysis is", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Diaphysis**: The diaphysis is the long shaft of a long bone. It is important to know that it contains a central cavity.

2. **Identifying the Cavity**: The central cavity within the diaphysis is known as the medullary cavity. This cavity is crucial for the function of the bone.

3. **Function of the Medullary Cavity**: The medullary cavity is primarily filled with bone marrow, which is essential for the production of blood cells. This is why it is also referred to as the marrow cavity.

4. **Analyzing the Options**:
- **Endosteum**: This is a thin membrane that lines the medullary cavity but is not the cavity itself.
- **Periosteum**: This is a dense layer of vascular connective tissue that envelops the bones except at the surfaces of the joints, and it is also not the cavity.
- **Both one and two**: Since neither the endosteum nor the periosteum is the hollow cavity, this option is incorrect.
- **Marrow cavity**: This is the correct term for the hollow cavity of the diaphysis.

5. **Conclusion**: The correct answer to the question is the "marrow cavity".

### Final Answer:
The hollow cavity of diaphysis is the **marrow cavity**.

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