The aggregated lymphatic nodules (noduli lymphatici aggregati; Peyer's patches; Peyer's glands; agminated follicles; tonsillæ intestinales) form circular or oval patches, from twenty to thirty in number, and varying in length from 2 to 10 cm.
They are largest and most numerous in the ileum. In the lower part of the jejunum they are small, circular, and few in number. They are occasionally seen in the duodenum.
They are placed lengthwise in the intestine, and are situated in the portion of the tube most distant from the attachment of the mesentery.
Each patch is formed of a group of solitary lymphatic nodules covered with mucous membrane, but the patches do not, as a rule, possess villi on their free surfaces.
They are best marked in the young subject, become indistinct in middle age, and sometimes disappear altogether in advanced life.
They are freely supplied with bloodvessels, which form an abundant plexus around each follicle and give off fine branches permeating the lymphoid tissue in the interior of the follicle. The lymphatic plexuses are especially abundant around these patches.