The Palatine Tonsils (tonsillæ palatinæ tonsil) are two prominent masses situated one on either side between the glossopalatine and pharyngopalatine arches.
Each tonsil consists fundamentally of an aggregation of lymphoid tissue underlying the mucous membrane between the palatine arches. The lymphoid mass, however, does not completely fill the interval between the two arches, so that a small depression, the supratonsillar fossa, exists at the upper part of the interval. Further, the tonsil extends for a variable distance under cover of the glossopalatine arch, and is here covered by a reduplication of mucous membrane; the upper part of this fold reaches across the supratonsillar fossa, between the two arches, as a thin fold sometimes termed the plica semilunaris; the remainder of the fold is called the plica triangularis. Between the plica triangularis and the surface of the tonsil is a space known as the tonsillar sinus; in many cases, however, this sinus is obliterated by its walls becoming adherent. From this description it will be apparent that a portion of the tonsil is below the level of the surrounding mucous membrane, i. e., is imbedded, while the remainder projects as the visible tonsil. In the child the tonsils are relatively (and frequently absolutely) larger than in the adult, and about one-third of the tonsil is imbedded. After puberty the imbedded portion diminishes considerably in size and the tonsil assumes a disk-like form, flattened from side to side; the shape; and size of the tonsil, however, vary considerably in different individuals.
The medial surface of the tonsil is free except anteriorly, where it is covered by the plica triangularis; it presents from twelve to fifteen orifices leading into small crypts or recesses from which numerous follicles branch out into the tonsillar substance.
The lateral or deep surface is adherent to a fibrous capsule which is continued into the plica triangularis. It is separated from the inner surface of the Constrictor pharyngis superior usually by some loose connective tissue; this muscle intervenes between the tonsil and the external maxillary artery with its tonsillar and ascending palatine branches. The internal carotid artery lies behind and lateral to the tonsil at a distance of 20 to 25 mm. from it.
The tonsils form part of a circular band of adenoid tissue which guards the opening into the digestive and respiratory tubes. The anterior part of the ring is formed by the submucous adenoid collections (lingual tonsil) on the posterior part of the tongue; the lateral portions consist of the palatine tonsils and the adenoid collections in the vicinity of the auditory tubes, while the ring is completed behind by the pharyngeal tonsil on the posterior wall of the pharynx. In the intervals between these main masses are smaller collections of adenoid tissue.