part of part_of develops from head mouth The proximal portion of the digestive tract, containing the oral cavity and bounded by the oral opening. In vertebrates, this extends to the pharynx and includes teeth, gums, lips, tongue and parts of the palate. adult mouth cavital oralis cavitas oris cavum oris mouth cavity oral region oral vestibule regio oralis rima oris stoma stomatodaeum vestibule of mouth vestibulum oris stomodeum ectodermal part of digestive tract