title: The thymus of the guinea fowl from the eighteenth day of incubation until maturity.
abstract: The thymus gland of the guinea fowl appeared as a series of pink, irregular-shaped lobes along the jugular veins. These lobes were 13 in number with seven on the right and six on the left side. The third and sixth lobes on the right side were the largest. The largest lobe measured about 20.0 x 5.0 mm while the smallest measured about 5.0 x 4.0 mm. Histologically, it was encircled by a thin layer of poorly stained connective tissue from which strands penetrated the thymic tissue giving incomplete lobules peripherally as early as day 18 of incubation. Lymphocytes and reticular epithelial cells were the two types of cells occurring at this time. Reticular epithelial cells were observed to be vacuolated especially towards the centre of the gland. Macrophages were observed in the thymus on day 20 of incubation for the first time. The blood vessels had accompanied the interlobular septa into the thymus. By day 21 of incubation, blood vessels had actually penetrated the thymic tissue but most of these vessels were of the capillary size. The cortex also became quite distinct from the medulla. At day 22, vacuolation ceased to appear in the cells at the cortical zone. Macrophages were still less than 10 in the slide. At day 23, most blood vessels were within the medulla and they displayed compressed lumina. Mitotic figures became a common site amongst the large lymphocytes and reticular epithelial cells. By day one post-hatch, lobulation of the thymus was still poor and macrophages became difficult to identify. The small and medium lymphocytes had outnumbered the large lymphocytes throughout the thymic tissue except at the most peripheral zone of the cortex. Fine vacuoles had reappeared within the cytoplasm of the reticular epithelial cells in the cortex. By day five, the distribution of blood vessels was almost uniform between the cortex and medulla. At three weeks post-hatch, plasma cells and red blood cells were seen in the stroma of the gland for the first time and most of the red blood cells occurred in the medulla.
authors.affiliation: Department of Veterinary Anatomy, Ahmadu Bello University, Zaria, Nigeria.
authors.forename: B I
authors.initials: BI
authors.lastname: Onyeanusi
authors.forename: J C
authors.initials: JC
authors.lastname: Onyeanusi
authors.forename: A N
authors.initials: AN
authors.lastname: Emma
authors.forename: C D
authors.initials: CD
authors.lastname: Ezeokoli
mesh_terms: D000818:Animals; D011200:Poultry / Q000196:embryology* / Q000254:growth & development*; D013950:Thymus Gland / Q000166:cytology / Q000196:embryology* / Q000254:growth & development*