**Core Concept**
The final common pathway for horizontal eye movement involves the coordinated action of several cranial nerves and brainstem structures. This complex process is mediated by the extraocular muscles, particularly the lateral rectus and medial rectus muscles, which are responsible for outward and inward movements of the eye, respectively.

**Why the Correct Answer is Right**
The correct answer is the **abducens nucleus** (CN VI), which is the final common pathway for horizontal eye movement. The abducens nucleus receives input from the contralateral frontal eye field and sends signals to the lateral rectus muscle through the abducens nerve (CN VI). This results in outward rotation of the eye. The abducens nucleus is also influenced by the vestibular system, which helps to maintain eye position during head movements.

**Why Each Wrong Option is Incorrect**
**Option A:** The **trochlear nucleus** (CN IV) is responsible for upward gaze and is not involved in horizontal eye movement.
**Option B:** The **oculomotor nucleus** (CN III) controls several extraocular muscles, including the medial rectus, but is not the final common pathway for horizontal eye movement.
**Option C:** The **trochlear nerve** (CN IV) is involved in upward gaze, not horizontal eye movement.

**Clinical Pearl / High-Yield Fact**
The abducens nucleus is the only cranial nerve nucleus that is located in the pons, making it a key landmark for identifying this brainstem region.

**Correct Answer: C. Abducens nucleus.**