palate) fibers from a branch of the facial nerve [VII] join the nerves in the pterygopalatine fossa, as do the sympathetics (mainly to blood vessels) ultimately derived from the T1 spinal cord level.
The greater and lesser palatine nerves descend through the pterygopalatine fossa and palatine canal to reach the palate (Fig. 8.276):
The greater palatine nerve travels through the greater palatine foramen and turns anteriorly to supply the hard palate and gingiva as far as the first premolar.
The lesser palatine nerve passes posteromedially to supply the soft palate.
The nasopalatine nerve also originates in the pterygopalatine fossa, but passes medially into the nasal cavity. It continues medially over the roof of the nasal cavity to reach the medial wall, then anteriorly and obliquely down the wall to reach the incisive canal in the anterior floor, and descends through the incisive canal and fossa to reach the inferior surface of the hard palate (Fig. 8.276).
The nasopalatine nerve supplies gingiva and mucosa adjacent to the incisors and canine.
The oral fissure is the slit-like opening between the lips that connects the oral vestibule to the outside (Fig. 8.277). It can be opened and closed, and altered in shape by the movements of the muscles of facial expression associated with the lips and surrounding regions, and by movements of the lower jaw (mandible).
The lips are entirely composed of soft tissues (Fig. 8.277B). They are lined internally by oral mucosa and covered externally by skin. Externally, there is an area of transition from the thicker skin that covers the face to the thinner skin that overlies the margins of the lips and continues as oral mucosa onto the deep surfaces of the lips.
Blood vessels are closer to the surface in areas where the skin is thin and as a consequence there is a vermilion border that covers the margins of the lips.
The upper lip has a shallow vertical groove on its external surface (the philtrum) sandwiched between two elevated ridges of skin (Fig. 8.277A). The philtrum and ridges are formed embryologically by fusion of the medial nasal processes.
On the inner surface of both lips, a fold of mucosa (the median labial frenulum) connects the lip to the adjacent gum.
The lips enclose the orbicularis oris muscle, neurovascular tissues, and labial glands (Fig. 8.277B). The small pea-shaped labial glands are between the muscle tissue and the oral mucosa and open into the oral vestibule.
A number of muscles of facial expression control the shape and size of the oral fissure. The most important of these is the orbicularis oris muscle, which encircles the orifice and acts as a sphincter. A number of other muscles of facial expression blend into the orbicularis oris or other tissues of the lips and open or adjust the contours of the oral fissure. These include the buccinator, levator labii superioris, zygomaticus major and minor, levator anguli oris, depressor labii inferioris, depressor anguli oris, and platysma (see pp. 897–899).
The oropharyngeal isthmus is the opening between the oral cavity and the oropharynx (see Fig. 8.271). It is formed: laterally by the palatoglossal arches; superiorly by the soft palate; and inferiorly by the sulcus terminalis of the tongue that divides the oral surface of the tongue (anterior two-thirds) from the pharyngeal surface (posterior one-third).
The oropharyngeal isthmus can be closed by elevation of the posterior aspect of the tongue, depression of the palate, and medial movement of the palatoglossal arches toward the midline.