**Core Concept**
The question is referring to a specific anatomical structure located in the nasal cavity, which plays a crucial role in the parasympathetic regulation of nasal secretion. This structure is responsible for the lacrimation (tear production) response, hence the term "gateway of tears."

**Why the Correct Answer is Right**
The correct answer is the infratrochlear nerve, which is a branch of the ophthalmic division of the trigeminal nerve (V1). The infratrochlear nerve carries preganglionic parasympathetic fibers that synapse in the nasal mucosa, leading to the release of acetylcholine, which stimulates the mucous glands to produce tears. This response is mediated by the muscarinic receptors (M3 subtype) present on the mucous glands.

**Why Each Wrong Option is Incorrect**
**Option A:** The external nasal branches of the anterior ethmoidal nerve are involved in the regulation of nasal secretion, but they are not the primary structure responsible for the lacrimation response.
**Option B:** The ciliary ganglion is a parasympathetic ganglion located near the eye, but it is not directly involved in the regulation of nasal secretion.
**Option C:** The facial nerve (cranial nerve VII) is responsible for the lacrimation response through its parasympathetic fibers, but it is not the "gateway of tears" in the context of the nasal cavity.

**Clinical Pearl / High-Yield Fact**
The lacrimation response is a classic example of a parasympathetic-mediated reflex, which is mediated by the release of acetylcholine from preganglionic fibers. This response is often used as a diagnostic tool to assess the integrity of the parasympathetic nervous system.

**Correct Answer: C. The infratrochlear nerve.**