Tongue is attached to the floor of buccal cavity by

The correct option/answer is frenulum.

To understand why this is the correct answer, let's break down the anatomy of the oral cavity and evaluate the given options:
1. Frenulum (specifically, lingual frenulum): This is a small fold of mucous membrane that extends from the floor of the mouth to the midline of the underside of the tongue. It functions to anchor the tongue to the floor of the buccal (oral) cavity while still allowing it to move freely during speaking, eating, and swallowing.
2. Falciform ligament: This is a structure in the abdominal cavity that attaches the liver to the anterior abdominal wall and diaphragm. It is not located in the mouth.
3. Lingual papilla: These are small, nipple-like structures on the upper surface (dorsum) of the tongue that contain taste buds. They do not attach the tongue to the floor of the mouth.
4. Mesentery: This is a fold of membrane that attaches the intestines to the posterior abdominal wall. Like the falciform ligament, it is located in the abdominal cavity, not the mouth.

Therefore, the tongue is attached to the floor of the buccal cavity by the frenulum.