The oral cavity is also known as the mouth. In it, chemical digestion of starch begins due to the enzyme ptyalin, present in saliva. It is actually the beginning of the food tube or digestive cavity. The mouth contains teeth for mechanical digestion of food and is lined with a mucous membrane made of epithelial cells. Its functions have to do with breathing, drinking and eating. The nasal cavity is located above and behind the nose. It is part of the respiratory system. Its function is to filter and warm air to almost body temperature. Cilia, microscopic hairs filter dust and germs and push this to the pharynx so that it may pass on to the stomach to be digested. The floor of the nasal cavity makes up the roof of the mouth. Therefore, they are in close proximity of one another.
The oral cavity is the area from the mouth to the back of the throat. The nasal cavity is located from the nose to the base of the cranium and above the oral cavity but separated by the palate. The oral cavity and nasal cavity are joined at the pharynx. Incoming air can be conducted through either the oral or nasal cavity to the pharynx.