These are extensions of the lacunae and are filled with extracellular fluid.

Options

A. Volkmann's canals
B. Haversian canals
C. Osteons
D. Canaliculi

Answer

To answer the question regarding the extensions of lacunae that are filled with extracellular fluid, we will analyze the options provided.

### Step-by-Step Solution:

1. **Understand the Question**: The question is asking for the structures that are extensions of lacunae and are filled with extracellular fluid.

2. **Analyze the Options**:
- **Voxman Canal**: This canal is known for transmitting blood vessels in the bone. It does not relate to lacunae or extracellular fluid. Thus, it is not the correct answer.
- **Haversian Canal**: This is the central canal of the bone that contains blood vessels. It is also not an extension of lacunae, so it is incorrect.
- **Osteon**: The osteon is the basic structural unit of bone. While it is related to bone structure, it does not specifically refer to the extensions of lacunae. Therefore, it is also incorrect.
- **Canaliculi**: These are indeed the extensions of lacunae. They are small channels that connect lacunae and are filled with extracellular fluid, allowing for nutrient exchange and communication between bone cells.

3. **Identify the Correct Answer**: Based on the analysis, the correct answer is **canaliculi**.

### Final Answer:
The correct answer is **canaliculi**.

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