Teeth is Termed the Vestibular Sulcus
The glossopharyngeal nerve leaves the cranium through the jugular foramen. It supplies sensory taste fibres to the posterior third of the tongue and sensory and motor fibres to the soft palate and pharynx. It also carries parasympathetic fibres to the auriculotemporal nerve and mandibular division of the trigeminal.
The hypoglossal nerve leaves the cranium through the hypoglossal canal. It supplies motor fibres to the intrinsic and extrinsic muscles of the tongue (except the palatoglossal muscle).
The oral cavity is bounded by the lips and cheeks anteriorly and it extends posteriorly to the palato-glossal and palato-pharyngeal arches (pillars of the fauces). The hard palate forms the roof of the oral cavity and the floor of the mouth forms the floor, this space being occupied by the tongue. The oral cavity also contains the upper and lower alveolar ridges which house the teeth. The area between the lips and alveolar ridge and teeth is termed the vestibular sulcus.
The lips contain the orbicularis oris muscle. They are covered by skin externally and mucous membrane internally; where the external surface meets the internal surface a distinct line may be seen, termed the vermillion border. The external red border of the lips is termed the vermillion zone. A shallow depression extending from the midline of the nose to the centre of the upper lip is called the philtrum. The naso-labial grooves are shallow depressions extending from the corner of the nose to the corner of the lips. Between the lower lip and the chin can be found a midline linear depression, the labio-mental groove.
The inner surface of the lip is tightly bound to connective tissue. At the midline, the upper and lower lips are attached to the alveolar ridges by a labial fraenum.
