**Core Concept**
The term "figure linearum labiorum rubroum" refers to a specific anatomical feature. **Oral commissures** and **vermilion borders** are key terms related to the lips.

**Why the Correct Answer is Right**
The correct answer is related to the appearance of the lips, specifically the linear or border aspect of the red part of the lips. This term is used to describe a particular characteristic of the **vermilion border**, which is the distinct border between the red part of the lip and the surrounding skin.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it does not relate to the specific term given.
**Option B:** Incorrect as it is unrelated to the description of lip anatomy.
**Option C:** Incorrect because it does not match the term "figure linearum labiorum rubroum".

**Clinical Pearl / High-Yield Fact**
The vermilion border is an important landmark in **facial anatomy** and **oral pathology**.

**Correct Answer:** Correct Answer: D. Vermilion border