Okay, let's tackle this question about the parotid duct. The user wants to know which muscle the parotid duct pierces. First, I need to recall the anatomy of the parotid gland and its duct. The parotid duct, also known as Stensen's duct, starts from the anterior border of the gland. I remember that it runs forward across the masseter muscle. So the key here is to identify which muscle it pierces.

The core concept here is the anatomy of the parotid duct. The duct's path is important for clinical reasons, like infections or stones causing blockage. The main muscle involved is the masseter. Let me make sure: the parotid duct does pass through the masseter muscle. Wait, does it pierce it or just pass over? No, I think it actually pierces the masseter to reach the oral cavity. So the correct answer should be masseter.

Now, the options. Let's say the options are A. Buccinator, B. Masseter, C. Temporalis, D. Sternocleidomastoid. The correct answer is B. Masseter. The other options are incorrect because the buccinator is more posterior, the temporalis is a different muscle, and sternocleidomastoid is in the neck.

Clinical pearl: Remembering that the parotid duct pierces the masseter is crucial for understanding the pathway of the duct, which is important in conditions like parotid sialadenitis. Also, the duct opens into the oral cavity via the parotid papilla on the upper molars. A mnemonic could be "Masseter makes the parotid duct pass through."

**Core Concept** The parotid duct (Stensen's duct) transports saliva from the parotid gland to the oral cavity. Its anatomical course involves piercing a specific facial muscle, which is critical for clinical understanding of parotid gland disorders.

**Why the Correct Answer is Right** The parotid duct originates at the anterior border of the parotid gland and descends obliquely across the masseter muscle. It pierces the **masseter** to reach the buccal mucosa, where it opens into the oral cavity at the parotid papilla opposite the upper second molar. This pathway is essential for normal salivary drainage and is a common site for sialolithiasis (salivary stones).

**Why Each Wrong Option is Incorrect**
**Option A: Buccinator** – The buccinator lies posterior to the duct and does not form a barrier it must pierce.
**Option C: Temporalis** – This muscle is superior and lateral to the parotid duct, not involved in its pathway.
**Option D: Sternocleidomastoid** – Located in the neck, this muscle is unrelated to parotid duct anatomy.

**Clinical Pearl / High-Yield Fact** Remember: *“Masseter makes the parotid duct pass through!”* The duct’s piercing of the masseter is a key landmark for diagnosing parotid gland obstructions. Sialolithiasis here often presents with postprandial swelling and pain.

**Correct Answer: B. Masseter**

✓ Correct Answer: A. Buccinator