I am a lobular structrue located between lungs behind sternum on the vental side of aorta and plays an important role in the development of the immune system. Identify me.

Answer

**Step-by-Step Solution:**

1. **Identify the Location**: The structure is described as being located between the lungs, behind the sternum, and on the ventral side of the aorta. This gives us a specific anatomical location to consider.

2. **Determine the Structure Type**: The description mentions that it is a lobular structure. This suggests that the organ has a divided or lobed appearance.

3. **Function in the Immune System**: The question states that this structure plays an important role in the development of the immune system. This indicates that the organ is likely involved in the production or maturation of immune cells.

4. **Connect Features to Known Organs**: Considering the location (between the lungs, behind the sternum) and the function (development of the immune system), we can narrow down the possibilities. The thymus gland is known to be located in this area and is crucial for the maturation of T lymphocytes.

5. **Confirm the Answer**: The thymus gland is indeed responsible for the development and maturation of T lymphocytes, which are essential for cell-mediated immunity. This confirms that the structure in question is the thymus gland.

6. **Consider Age-Related Changes**: It is also important to note that the thymus gland decreases in size with age, which can lead to a weakened immune response in older individuals.

**Final Answer**: The structure described in the question is the **thymus gland**.

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