**Core Concept**
Tubercles of Montgomery are small, Montgomery's tubercles are pigmented papules found on the areola of the nipple in lactating women. They are a normal anatomical variation that is thought to be involved in the expression of milk during lactation.

**Why the Correct Answer is Right**
The presence of Montgomery's tubercles is due to the proliferation of sebaceous glands and ducts in the areola, which becomes more pronounced during pregnancy and lactation. This increase in glandular tissue is thought to aid in the expression of milk by providing a lubricating effect on the nipple-areolar complex. The tubercles are also highly vascularized, which may contribute to their pigmentation.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because tubercles of Montgomery are not typically found on the skin of the breast itself, but rather on the areola surrounding the nipple.

**Option B:** Incorrect because while tubercles of Montgomery are a normal variation, they are not typically found on the skin of the nipple.

**Option C:** Incorrect because while there are other normal anatomical variations of the breast, tubercles of Montgomery are specifically associated with the areola.

**Clinical Pearl / High-Yield Fact**
Montgomery's tubercles are a normal finding in lactating women and are not a cause for concern unless they are accompanied by other unusual symptoms or signs.

**Correct Answer: D. Areola. Montgomery's tubercles are pigmented papules found on the areola of the nipple in lactating women.**