**Core Concept**
Pterygium is a common ocular surface disorder characterized by the growth of a fibrovascular tissue on the conjunctiva, often extending onto the cornea. The corneal involvement in pterygium is primarily due to the invasion of fibroblasts and vascularization, leading to the formation of a triangular-shaped lesion.

**Why the Correct Answer is Right**
The layer of cornea most often involved in pterygium is the **stroma**. This is because the stromal layer is the thickest and most vascularized part of the cornea, making it an ideal site for the invasion of fibroblasts and vascularization. The stroma is composed of collagen fibers and keratocytes, which can be replaced by fibrovascular tissue in pterygium. The Bowman's layer and the epithelium are less commonly involved due to their relative avascularity and compact structure.

**Why Each Wrong Option is Incorrect**
**Option A:** The **endothelium** is the innermost layer of the cornea and is not typically involved in pterygium.
**Option B:** The **Descemet's membrane** is a thin, acellular layer separating the endothelium from the stroma, and it is not a primary site of involvement in pterygium.
**Option C:** The **Bowman's layer** is a dense, acellular layer between the epithelium and the stroma, but it is less commonly involved in pterygium due to its compact structure.

**Clinical Pearl / High-Yield Fact**
Pterygium is more common in individuals with prolonged exposure to ultraviolet radiation, particularly in tropical and subtropical regions.

**Correct Answer:** C.