**Core Concept**
The gland of Moll is a minor salivary gland located in the oral cavity, and it plays a role in the secretion of mucin and other substances that contribute to the lubrication of the mouth.

**Why the Correct Answer is Right**
The gland of Moll is a type of minor salivary gland that is found in the mucous membrane of the lower lip. It is located near the corner of the mouth and opens into the oral cavity through a small duct. This gland is one of the many minor salivary glands that contribute to the overall secretion of saliva in the mouth, which is essential for lubrication, taste, and digestion.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the gland of Moll is not located on the tongue.
**Option B:** This option is incorrect because the gland of Moll does not open into the nasal cavity.
**Option C:** This option is incorrect because the gland of Moll is not a major salivary gland and does not open into the submandibular gland.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that minor salivary glands like the gland of Moll can be involved in various oral pathologies, such as sialadenitis and sialolithiasis.

**Correct Answer: D. The oral cavity.