The tonsils consist of aggregations of lymphatic nodules that are clustered around the posterior opening of the oral and nasal cavities.
Lymphatic tissue is organized into a tonsillar (Waldeyer’s) ring of immunologic protection located at the shared entrance to the digestive and respiratory tracts. This lymphatic tissue surrounds the posterior orifice of the oral and nasal cavities and contains aggregates of lymphatic nodules that include the following:  Palatine tonsils, or simply the tonsils, which are located at either side of the entrance to the oropharynx between the palatopharyngeal and palatoglossal arches  Tubal tonsils, which are located in the lateral walls of the nasopharynx posterior to the opening of the auditory tube  Pharyngeal tonsil, or adenoid, which is located in the roof of the nasopharynx  Lingual tonsil, which is located at the base of the tongue
The oral cavity is lined by the oral mucosa that consists of masticatory mucosa, lining mucosa, and specialized mucosa.
The masticatory mucosa is found on the gingiva (gums) and the hard palate (Fig. 16.1). It has a keratinized and, in some areas, a parakeratinized stratifed squamous epithelium (Fig. 16.2). Parakeratinized epithelium is similar to keratinized
FIGURE 16.1 • Roof of oral cavity. The hard palate, which contains bone, is bisected into right and left halves by a raphe. Anteriorly, in the fatty zone, the submucosa of the hard palate contains adipose tissue; posteriorly, in the glandular zone, there are mucous glands within the submucosa. Neither the raphe nor the gingiva contains a submucosa; instead, the mucosa is attached directly to the bone. The soft palate has muscle instead of bone, and its glands are continuous with those of the hard palate in the submucosa. (Based on Bhaskar SN, ed. Orban’s Oral Histology and Embryology. St. Louis: CV Mosby, 1991.)
FIGURE 16.2 • Stratified squamous epithelium of the hard palate. This photomicrograph shows a transition in the oral mucosa from a stratified squamous epithelium (on the right) to a stratified squamous parakeratinized epithelium (on the left). The flattened surface cells of the keratinized epithelium are devoid of nuclei. The layer of keratohyalin granule–containing cells is clearly visible in this type of epithelium. The flattened surface cells of the parakeratinized epithelium display the same characteristics as the keratinized cells, except they retain their nuclei, i.e., they are parakeratinized. In addition, note the paucity of keratohyalin granules present in the subsurface cells. 380.
epithelium except that the superficial cells do not lose their nuclei and their cytoplasm does not stain intensely with eosin (Plate 48, page 557). The nuclei of the parakeratinized cells are pyknotic (highly condensed) and remain until the cell is exfoliated (see Fig. 16.2). The keratinized epithelium of the masticatory mucosa resembles that of the skin but lacks a stratum lucidum. The underlying lamina propria consists of a thick papillary layer of loose connective tissue that contains blood vessels and nerves, some of which send bare axon endings into the epithelium as sensory receptors, and some of which end in Meissner’s corpuscles. Deep to the lamina propria is a reticular layer of more-dense connective tissue.