الفهرس 
Approval Sheet
Cloacal bursaOnly 14 pages are availabe for public view
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Abstract
A well developed bursa formed of mucosa, musculosa and serosa. Its lamina propria was lymphoid in nature. After hatching, the bursa continued to grow and become fully developed at the 30th day posthatching. It appeared as a blind sac whose lumen was reduced by the presence of about 12-13 mucosal folds. It was lined with tail columnar or pseudo stratified columnar epithelium. The lamina propria forming also the core of the folds contained a large number of lymphoid follicles. Each follicle possessed an outer corona and a germinal center with epithelial remnants at their junctional area. Birds examined at the ages 6 weeks indicated the start of physiological regression of the bursa. The follicles were decreased in size, the Iymphocytes were depleted and the interfollicular stroma became thicker and more fibrous. Fibrosis of the lymphoid follicles was frequently seen in some sections at the age of 30 weeks. The thymus of one week old chicks appeared as multi lobulated organ. Its interstitial stroma was formed of a network of epithelial reticular cells and reticular fibers. Distinction between the cortical and medullary tissues was not clear. Thymic corpuscles were frequently seen in the medulla. At the age of 4 weeks, the cortex became more clearly distinct from the medulla due to its greater population with small Iymphocytes noticeable degenerative changes could be observed in the thymocytes and in the epithelial reticular cells of the thymus of 18 weeks old chickens and collagen fibers start to increase in amount. Degeneration of the Iymphocytes was characterized by pleomorphism while the epithelial reticular cells tended to aggregate forming masses of cells in varying degrees of regression. Many eosinophils and macrophages were frequently seen. The thymus of 21 weeks old chickens appeared smaller in size. The degenerative changes in the thymic cells became more advanced. The cortex became narrower and its distinction from the medulla was less evident.