**Core Concept**
The medial wall of the orbit is formed by the sphenoid bone, ethmoid bone, and lacrimal bone. These bones contribute to the structure of the orbit and provide a passage for important nerves and blood vessels.

**Why the Correct Answer is Right**
The zygoma bone, also known as the zygomatic bone, forms the lateral wall of the orbit, but it does not contribute to the medial wall. The medial wall is primarily formed by the lamina papyracea of the ethmoid bone, the sphenoid bone's orbital plate, and the lacrimal bone. The lacrimal bone specifically forms the posterior part of the medial wall and houses the nasolacrimal duct.

**Why Each Wrong Option is Incorrect**
**Option A:** The ethmoid bone does contribute to the medial wall of the orbit, specifically the lamina papyracea which forms the anterior part of the medial wall.
**Option B:** The lacrimal bone also contributes to the medial wall of the orbit, forming the posterior part.
**Option C:** The frontal bone contributes to the roof of the orbit, but it does not form part of the medial wall.

**Clinical Pearl / High-Yield Fact**
Remember the acronym **SLEN** to recall the bones that contribute to the medial wall of the orbit: Sphenoid, Lacrimal, Ethmoid, and Nasal (the nasal conchae contribute to the medial wall as well).

**✓ Correct Answer: D. Zygoma**