The connotation given to the term fauces varies. Though complete agreement exists as to the general region to which the term refers, the precise contents and boundaries of this region vary between sources. In general, the area covers the space from the oral cavity into the pharynx. By most authors, the designation isthmus of the fauces, or oropharyngeal isthmus, is taken to mean the aperture by which the mouth communicates with the pharynx (i.e., the dividing line between the oral cavity and the oropharynx). The boundaries of this isthmus are the soft palate superiorly, the dorsum of the tongue in the region of the terminal sulcus inferiorly, and the left and right palatoglossal folds, also known as the anterior pillars of the fauces, which rise archlike on each side in the posterior limit of the oral cavity.
Closer to the oropharynx, a second arch is formed by the palatopharyngeal folds, also called the posterior pillars of the fauces. As a result of the projecting prominence of the anterior and posterior folds on each side, a fossa (tonsillar fossa or tonsillar sinus) comes into existence, which houses the palatine tonsil. On the free surface of this oval mass, which may bulge medially into the cavity of the pharynx for varying distances, 12 to 15 orifices (fossulae tonsillares) can be recognized. These are the openings of the tonsillar crypts. The latter branch and extend deeply into the substances of the tonsils. Several quite variable folds may overlap the medial surface of the tonsils in different degrees. Most frequently found is a triangular fold located anteriorly and inferiorly to the tonsils. Also, between the superior portions of the palatoglossal and palatopharyngeal folds, one may encounter frequently a supratonsillar fold that contains tonsillar tissue, a fact that has prompted some authors to call the recess below this fold the infratonsillar recess (or fossa) and others to designate it as “supratonsillar.” The lateral surface of the tonsil has a fibrous capsule, which is separated by some loose connective tissue from the superior constrictor muscle of the pharynx and, to a lesser and variable degree, from the palatopharyngeus muscle that sits deep to the fold of the same name.
The chief blood supply of the tonsil is the tonsillar branch of the facial artery, but the tonsillar branches of the lesser palatine, ascending palatine, ascending pharyngeal, and dorsal lingual arteries also participate in the arterial blood supply. Lymphatic fluid from the tonsil drains primarily to the jugulodigastric lymph node of the superior deep cervical group. The tonsil is innervated primarily by the glossopharyngeal nerve, though a few branches of the lesser palatine nerves also enter the tonsils.
A stratified squamous epithelium covers the tonsil and also lines the crypts, where it may be obscured by lymphocyte infiltration. The mass of the tonsils consists of lymphatic (lymphoid) tissue, which presents itself mostly in the form of lymph nodules or follicles, which, particularly in younger individuals, contain many germinal centers. Expansions from the above-mentioned fibrous capsule on the lateral tonsillar surface enter the lymphoid tissue, forming septa between the follicles surrounding the adjacent crypts.
Present at birth and increasing in size rapidly during the first few years of life, the tonsils usually decrease in size about puberty and may become atrophic in old age.