**Core Concept**
The intraoral approach to expose the submandibular duct involves a precise dissection through the mucous membrane to access the duct without necessitating a more extensive surgical incision. This method is preferred to minimize postoperative morbidity and scarring.

**Why the Correct Answer is Right**
In the intraoral approach, the surgeon primarily incises through the mucous membrane to access the submandibular duct. The mucous membrane covering the duct is the primary barrier to be overcome. This is a delicate procedure, as the duct is situated beneath the mucous membrane, and the surrounding tissue is relatively loose and easily dissectable. The mucous membrane is the primary tissue that needs to be incised to access the duct, making option A the correct answer.

**Why Each Wrong Option is Incorrect**
**Option B:** The genioglossus muscle is not typically involved in the intraoral approach to expose the submandibular duct. This muscle is involved in tongue movement and is not directly related to the duct's anatomical location.

**Option C:** The mylohyoid muscle is not necessary to be cut through in the intraoral approach to expose the submandibular duct. This muscle forms the floor of the oral cavity and is not directly related to the duct's location.

**Option D:** The hyoglossus muscle is not involved in the intraoral approach to expose the submandibular duct. This muscle is involved in tongue movement and is not directly related to the duct's anatomical location.

**Clinical Pearl / High-Yield Fact**
In the intraoral approach to expose the submandibular duct, it is essential to identify the duct's location carefully to avoid damaging surrounding structures. The duct is situated beneath the mucous membrane, and incising through this membrane is the primary step in accessing the duct.

**✓ Correct Answer: A. Mucous membrane only**