The tonsils are lumps of lymphoepithelial tissue surrounding the exits of the oral and nasal spaces into the pharynx (throat). They form a circle and have a protective function by early activation of specific defense mechanisms. The tonsils form the pharyngeal circle of Waldeyer, which consists of the unpaired pharyngeal tonsil in the roof of the pharynx, the paired palatine tonsils on each side of the palatine arch, and the lingual tonsil in the retrolingual region. There is additional lymphatic tissue in the lateral wall of the pharynx which, at the entrance to the Eustachian tube, is condensed into the tonsilla tubaria.
The lymphoid tissue in the tonsils consists of aggregated lymph follicles lying directly beneath the covering epithelium, the surface of which is deeply fissured by crypts. The lymphocytes (type of leukocytes) immigrate into the intercellular gaps between the epithelial cells. In the crypts there are plugs of detritus from shed epithelial cells and leukocytes. The tonsil is demarcated from its surroundings by a tout fibrous capsule which allows to be surgically removed. The tonsil is covered by stratified epithelium.