**Core Concept**
The cornea is a complex structure composed of multiple layers, each derived from a distinct embryonic germ layer. Understanding the embryological origin of the cornea's layers is crucial for grasping its anatomy and pathophysiology.

**Why the Correct Answer is Right**
The stroma of the cornea is the thickest layer, accounting for approximately 90% of its thickness. It is composed of densely packed collagen fibrils, which provide the cornea's rigidity and transparency. The mesoderm, specifically the neural crest-derived mesenchyme, gives rise to the corneal stroma. This is achieved through the migration of mesenchymal cells from the neural crest into the surface ectoderm-derived corneal epithelium, where they differentiate into keratocytes, the primary cellular components of the corneal stroma.

**Why Each Wrong Option is Incorrect**
**Option A:** Neural ectoderm is responsible for the development of the lens and retina, not the corneal stroma.
**Option B:** Surface ectoderm gives rise to the corneal epithelium and anterior part of the lens, but not the stroma.
**Option D:** While the neural crest does contribute to the development of the cornea, specifically through the formation of the corneal epithelium and the innervation of the cornea, it is not the primary source of the corneal stroma.

**Clinical Pearl / High-Yield Fact**
The corneal stroma's avascular nature and its dependence on the limbal stem cells for maintenance make it susceptible to injury and disease. Understanding the embryological origin of the cornea's layers is essential for grasping the pathophysiology of corneal disorders and developing effective treatment strategies.

**✓ Correct Answer: C. Mesoderm**