The Haversian system is related in mammals to :

Options

A. nervous system
B. skeletal system
C. respiratory system
D. urino-genital system

Explanation

### Step-by-Step Solution:

1. **Understanding the Haversian System**: The Haversian system, also known as the osteon, is the structural unit of compact bone. It consists of a central canal surrounded by concentric rings of bone matrix.

2. **Components of the Haversian System**: The Haversian system includes:
- **Haversian Canal**: The central canal that contains blood vessels and nerves.
- **Lamellae**: Concentric rings of bone matrix surrounding the Haversian canal.
- **Lacunae**: Small spaces within the lamellae that house osteocytes (bone cells).

3. **Relation to Body Systems**: The question asks which body system the Haversian system is related to among the options provided:
- **Nervous System**: Involves the brain, spinal cord, and nerves.
- **Skeletal System**: Comprises bones and muscles.
- **Respiratory System**: Includes the trachea, alveoli, and lungs.
- **Urinogenital System**: Combines the excretory and reproductive systems.

4. **Identifying the Correct System**: Since the Haversian system is a structural component of bone, it is directly related to the skeletal system. The other systems listed do not involve bones.

5. **Conclusion**: Therefore, the Haversian system is related to the **skeletal system** in mammals.

### Final Answer:
The Haversian system is related to the **skeletal system** in mammals.

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