Histologically, the wall of the alimentary canal shows four distinct layers (from the lumen moving out): mucosa, submucosa, muscularis externa, and either a serous membrane or an adventitia.

Identification of the submucosa plays an important role in diagnostic and therapeutic endoscopy, where special fibre-optic cameras are used to perform procedures on the gastrointestinal tract.

To confirm their findings, they performed fixed samples of bile duct into a freezing media in order to conserve the shape of the submucosa.

They then performed a histological analysis and with several staining techniques, they described the submucosa as a network of collagenous bands separating open, formerly fluid-filled spaces.

However, these cells are devoid of ultrastructural features indicative of endothelial differentiation, including pinocytotic vesicles and Weibel-Palade bodies.