Final answer:
The oral vestibule is the part of the mouth lying central to the teeth and is bordered externally by the cheeks and lips, while internally by the gums and teeth. It is part of the oral cavity, which also includes the hard palate, a bony structure pivotal for digestion and separation of oral and nasal cavities.
Step-by-step explanation:
The structure referred to in the question is the oral vestibule. It is the part of the mouth that lies central to the teeth, and is bounded externally by the cheeks and lips, and internally by the gums and teeth. The oral vestibule is just one part of the larger oral cavity, also known as the buccal cavity, which includes various structures such as the cheeks, tongue, and palate that frame the mouth. The hard palate and soft palate constitute the roof of the oral cavity, with the hard palate serving as a septum between the oral and nasal cavities and a shelf for the tongue during the digestive process. The hard palate is a bony structure formed by the palatine process of the maxillary bones and the horizontal plate of the palatine bones, while the soft palate is made up mainly of skeletal muscle and is located toward the back of the roof of the mouth.