**Core Concept**
Fordyce's spots, also known as Fordyce granules, are small, yellowish or whitish papules found on the lips, cheeks, and sometimes the genital area. They are a result of the ectopic presence of sebaceous glands, which are normally found in the skin.

**Why the Correct Answer is Right**
The correct answer is related to the ectopic presence of sebaceous glands. Sebaceous glands are responsible for producing sebum, an oily substance that helps to lubricate the skin. In the case of Fordyce's spots, these glands are found in areas where they are not typically located, such as on the lips and cheeks. This leads to the formation of small, visible papules.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to Fordyce's spots. While mucous glands are present in the oral cavity, they are not responsible for the formation of Fordyce's spots.

**Option B:** This option is incorrect because apocrine glands are primarily found in the axillary and genital areas and are not related to Fordyce's spots.

**Option C:** This option is not correct because eccrine glands are primarily found in the skin and are responsible for sweating, not the formation of Fordyce's spots.

**Clinical Pearl / High-Yield Fact**
Fordyce's spots are a benign condition and do not require treatment. They can be distinguished from other oral lesions by their characteristic yellowish or whitish appearance.

**Correct Answer:** D. Sebaceous glands.