As in the skin, the depth and number of connective tissue papillae contribute to the relative immobility of the masticatory mucosa, thus protecting it from frictional and shearing stress. At the midline of the hard palate, in the palatine raphe, the mucosa adheres firmly to the underlying bone. The reticular layer of the lamina propria blends with the periosteum, and thus there is no submucosa. The same is true of the gingiva. Where there is a submucosa underlying the lamina propria on the hard palate (see Fig. 16.1), it contains adipose tissue anteriorly (fatty zone) and mucous glands posteriorly (glandular zone) that are continuous with those of the soft palate. In the submucosal regions, thick collagenous bands extend from the mucosa to the bone.
Lining mucosa is found on the lips, cheeks, alveolar mucosal surface, floor of the mouth, inferior surfaces of the tongue, and soft palate. At these sites it covers striated muscle (lips, cheeks, and tongue), bone (alveolar mucosa), and glands (soft palate, cheeks, inferior surface of the tongue). The lining mucosa has fewer and shorter papillae so that it can adjust to the movement of its underlying muscles.
Generally, the epithelium of the lining mucosa is nonkeratinized, although in some places it may be parakeratinized. The epithelium of the vermilion border of the lip (the reddish portion between the moist inner surface and the facial skin) is keratinized. The nonkeratinized lining epithelium is thicker than keratinized epithelium. It consists of only three layers:  Stratum basale, a single layer of cells resting on the basal lamina  Stratum spinosum, which is several cells thick  Stratum superfciale, the most superficial layer of cells, also referred as the surface layer of the mucosa
The cells of the mucosal epithelium are similar to those of the epidermis of the skin and include keratinocytes, Langerhans’ cells, melanocytes, and Merkel’s cells.
The lamina propria contains blood vessels, nerves that send bare axon endings into the basal layers of the epithelium, and encapsulated sensory endings in some papillae. The sharp contrast between the numerous deep papillae of the alveolar mucosa and the shallow papillae in the rest of the lining mucosa allows easy identification of the two different regions in a histologic section.
A distinct submucosa underlies the lining mucosa except on the inferior surface of the tongue. This layer contains large bands of collagen and elastic fibers that bind the mucosa to the underlying muscle; it also contains the many minor salivary glands of the lips, tongue, and cheeks. Occasionally, sebaceous glands not associated with a hair follicle are found in the submucosa just lateral to the corner of the mouth and in the cheeks opposite the molar teeth. They are visible to the eye and are called Fordyce spots. The submucosa contains the larger blood vessels, nerves, and lymphatic vessels that supply the subepithelial neurovascular networks in the lamina propria throughout the oral cavity.
Specialized mucosa is associated with the sensation of taste and is restricted to the dorsal surface of the tongue. It contains papillae and taste buds responsible for generating the chemical sensation of taste.