Bursa of Fabricius
Cross section of the bursa of Fabricius of a chicken (HE): overview 2
The wall of the bursa of Fabricius consists of a capsule (capsula bursalis) and a mucosal layer. The mucosa forms folds (plicae bursales), the number and length of which varies with species (chicken: 12 folds mostly).
In most birds, the lymphoid tissue in the folds is organized into follicles (folliculi bursales), separated by sparse connective tissue.