**Core Concept**
A ranula is a type of mucocele that occurs on the floor of the mouth, typically resulting from the obstruction of the sublingual gland or duct. The surgical excision of a ranula involves the removal of the mucocele and the underlying gland or duct.

**Why the Correct Answer is Right**
During the surgical excision of a ranula, the submandibular duct is at risk of injury. This is because the submandibular duct is located in close proximity to the ranula and may be inadvertently damaged during the procedure. The submandibular duct carries saliva from the submandibular gland to the oral cavity, and injury to this duct can result in saliva leakage or fistula formation.

**Why Each Wrong Option is Incorrect**
**Option A:** The lingual vein is not typically injured during the excision of a ranula, as it is not in close proximity to the surgical site.
**Option B:** The lingual artery is also not typically injured during the excision of a ranula, as it is located more superficially and is not directly involved in the surgical field.
**Option D:** The parotid duct is not at risk of injury during the excision of a ranula, as it is located in the cheek and is not related to the sublingual gland or duct.

**Clinical Pearl / High-Yield Fact**
It is essential for surgeons to carefully identify and preserve the submandibular duct during the excision of a ranula to avoid complications such as saliva leakage or fistula formation.

**✓ Correct Answer: C. Submandibular duct**