ABSTRACT
Background: The Thymus is a lymphatic organ that exhibits certain unique structural features. The supportingreticular stroma arises from endodermal epithelium and produces a cellular reticulum. Lymphocytes are derivedfrom haematopoietic stem cells.Materials and methods: The present study was carried out with 20 human foetuses of gestational age varyingfrom 10 to 31weeks in the Department of Anatomy,Thanjavur medical college, Thanjavur. Histogenesis of variouscomponents of thymus was studied after staining with Hematoxylin and Eosin.Results: Lymphocytes appear by 10th week.Lobulation started appearing by 12th week and completed by 15thweek.Corticomedullary differentiation started by 15th week, and become more distinct by18th week. Blood vesselswere seen by 10th week and macrophages by 12th week. Hassall’s corpuscles appeared by 15th week. The numberand size of HC increased between 18 and 24 weeks.Conclusion: Precise knowledge of the histogenesis and histodifferentiation of the various components of thenormal thymus is essential in analyzing the different pathologies like thymic neoplasia, myasthenia gravis andcertain other autoimmune disorder