**Core Concept**
The superior oblique muscle is one of the six extraocular muscles responsible for eye movement. It plays a crucial role in controlling the rotation of the eyeball, particularly in the movement of the eye downward and inward. The innervation of this muscle is essential for understanding its function and potential disorders.

**Why the Correct Answer is Right**
The superior oblique muscle is supplied by the trochlear nerve (cranial nerve IV), which is the thinnest and longest of the cranial nerves. The trochlear nerve originates from the midbrain and courses laterally to reach the superior oblique muscle, which it innervates. This innervation is critical for the muscle's function, as it enables the eye to move downward and inward. The trochlear nerve is also unique in that it has the longest intracranial course of any cranial nerve, making it susceptible to injury.

**Why Each Wrong Option is Incorrect**
**Option A:** The oculomotor nerve (cranial nerve III) supplies four of the six extraocular muscles, but not the superior oblique muscle.
**Option B:** The abducens nerve (cranial nerve VI) supplies the lateral rectus muscle, which is responsible for outward gaze, not downward and inward movement.
**Option C:** The trigeminal nerve (cranial nerve V) is responsible for sensory and motor functions related to the face, but not the innervation of the extraocular muscles.

**Clinical Pearl / High-Yield Fact**
The trochlear nerve is particularly susceptible to injury due to its long intracranial course, making it a common site for compression or damage, particularly in cases of head trauma or tumors.

**Correct Answer: C. The trochlear nerve (cranial nerve IV).**