buccal vestibule
The buccal vestibule is the space external to teeth and gums and internal to lips and cheeks. The proportion of its walls formed by the lips varies according to species depending upon their feeding action. The horse like most herbivores has a relatively small opening. The buccal vestibule opens to the outside rostrally via a U shaped slit the oral fissure. When the mouth is closed the buccal vestibule and the mouth cavity proper connect via spaces between and behind the teeth. These allow free communication between the two sides of the vestibule. Several salivary ducts open into the dorso caudal part of the vestibule: Parotid gland - opens into the cheek on the small parotid papilla, opposite to the caudal part of upper 4 th premolar teeth. Zygomatic gland - the main duct opens in the caudal part of the upper 1 st molar tooth on a small papilla near the vestibular fornix. Submucous glands - minimal in number, confined to the lower lip and adjacent part of the cheek. Secretion occurs through about 10 openings located near the fornix of the vestibule.