The science diagram is about the oral cavity. A scientific diagram is a picture which shows exactly how an experiment has been set up. They aren't supposed to look like realistic sketches and are drawn in two dimensions. They need to be very clear, precise and easy to understand. In human anatomy, the mouth is the first portion of the alimentary canal that receives food and produces saliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth.