• The spleen of chickens is covered by a muscular capsule, but there are no trabeculae.
• The areas of the red and white pulp are less distinct than in mammals.

White Pulp
• The white pulp spreads out diffusely throughout the entire spleen
• is formed primarily by small lymphocytes.
• It contains sheeted arteries and occasionally lymphatic nodules.

Red Pulp
• The red pulp is formed by venous sinuses and anastomosing cords of reticular cells, macrophages, lymphocytes and haematids.

• As in mammals, the thymus is organized in incompletely separated lobules of cortical and medullar tissue.

• The typical Hassal Corpuscles, similar to those found in mammals, are not frequently observed.
• Instead, diffuse forms of Hassal’s corpuscles, called reticular structures, are abundant in the medulla.
• There are also myoid cells, characterized by a fibrous cytoplasm, in the medulla.

• Each follicle, composed of lymphatic tissue, divides itself into a cortex and medulla.
• A layer of undifferentiated epithelial cells occupy the border of the medulla, que é separada do córtex por uma camada capilar.
• The Bursa of Fabricius is lined by a pseudostratified epithelial, except at the apex of each follicle that is covered by an epithelial tuft of simple columnar cells.