**Core Concept**
Little's area, also known as Kiesselbach's plexus, is a vascular region in the anterior part of the nasal septum. It is a common site for nasal bleeding (epistaxis) due to its rich blood supply from multiple arteries. Understanding the blood vessels that contribute to Little's area is crucial for identifying the source of nasal bleeding.

**Why the Correct Answer is Right**
The posterior ethmoidal artery primarily supplies the posterior part of the nasal septum and the superior part of the nasal cavity. In contrast, the arteries listed in options A, B, and C (septal branch of the facial artery, anterior ethmoidal artery, and sphenopalatine artery) all contribute to the formation of Little's area. The sphenopalatine artery is the main artery that supplies blood to the nasal cavity and is a significant contributor to Little's area. The anterior ethmoidal artery also contributes to the nasal septum and is involved in the formation of Little's area.

**Why Each Wrong Option is Incorrect**
* **Option A:** The septal branch of the facial artery does contribute to Little's area by supplying blood to the anterior part of the nasal septum.
* **Option B:** The anterior ethmoidal artery contributes to the formation of Little's area by supplying blood to the nasal septum.
* **Option C:** The sphenopalatine artery is a major contributor to Little's area, supplying blood to the nasal cavity and the nasal septum.

**Clinical Pearl / High-Yield Fact**
It is essential to identify the source of nasal bleeding (epistaxis) to provide proper treatment. Knowing the blood vessels that contribute to Little's area can help in localizing the source of bleeding and guiding treatment.

**✓ Correct Answer:** D. Posterior ethmoidal artery