**Core Concept**
The parotid gland is the largest of the salivary glands, located in the preauricular region of the neck. Its duct, the parotid duct (Stensen’s duct), opens into the mouth opposite the upper second molar tooth, and it develops from the oral ectoderm during embryogenesis.

**Why the Correct Answer is Right**
The parotid duct (Stensen’s duct) opens into the mouth just opposite the upper second molar tooth, which is a well-documented anatomical landmark. This location is critical for clinical assessment and surgical planning. The duct passes through the masseter muscle, but it does not pierce it (Option B is false). The parotid gland develops from the oral ectoderm, not the neural crest (Option C is false). Secretomotor innervation comes from the facial nerve (CN VII), which supplies parasympathetic fibres to the gland (Option D is true — but not the best choice here). However, Option A is the most accurate and clinically significant statement.

**Why Each Wrong Option is Incorrect**
Option B: The parotid duct runs *parallel* to the masseter muscle and *passes through* it, but it does not *pierce* it. This is a common misconception.
Option C: The parotid gland develops from the **oral ectoderm**, not the neural ectoderm or mesoderm. This is a fundamental error in embryology.
Option D: While secretomotor fibres *do* originate from the facial nerve, this is not the most accurate statement about the parotid gland’s anatomy. The question asks for a *true* statement, and A is more anatomically precise and clinically relevant.

**Clinical Pearl / High-Yield Fact**
Always remember: The parotid duct opens **opposite the upper second molar** — a key landmark for diagnosing sialolithiasis or performing parotid surgery. This is a classic exam trap — many students confuse it with the lower molar or the mandibular angle.

✓ Correct Answer: A. Duct opens opposite to upper 2nd molar tooth