**Core Concept**
The nasal septum is a vertical structure that divides the nasal cavity into right and left sides. It is formed by bones and cartilage, including the perpendicular plate of the ethmoid, vomer, and nasal bone, but not by the lateral cartilage.

**Why the Correct Answer is Right**
The lateral cartilage (also known as the lateral cartilage of the nose) is part of the external nasal structure and forms the lateral wall of the nose, not the nasal septum. The nasal septum is composed of the perpendicular plate of the ethmoid bone, the vomer, and the nasal bone. The lateral cartilage is located in the external nasal framework and does not contribute to the septum.

**Why Each Wrong Option is Incorrect**
Option A: The perpendicular plate of the ethmoid bone forms the anterior and medial part of the nasal septum and is a key component.
Option B: The vomer is a thin, posterior cartilage that forms the posterior part of the nasal septum.
Option C: The nasal bone contributes to the anterior portion of the nasal septum, especially in the midline.

**Clinical Pearl / High-Yield Fact**
Remember: The nasal septum is made of **bone and cartilage**, but only the **vomer, perpendicular plate of ethmoid, and nasal bone** form it. The **lateral cartilage** is a separate structure and is not part of the septum—this is a common exam trap.

✓ Correct Answer: D. Lateral cailage