author(s)
MS Islam, M Kamruzzaman, MS Rahman, KA Ferdous, MSB Juli and MH Kabir

abstract
The experiment was carried out in the Laboratory of Anatomy and Histology, Hajee Mohammad Danesh Science and Technology University. Topology and histology were performed of the bursa of Fabricius and thymus of broiler chicken. The mean length, diameter and weight of the bursa and thymus were lower at day-1 (D1) stage and increased gradually at day-35 stage (D35).With increasing age, the bursa became larger with the plicae getting taller and thicker, which contained an enormous number of large polyhedral primary and secondary lymphoid follicles. It was found that the growth rates of bursa of Fabricius from day-1(D1) to day-21(D21) increased gradually but after D21 the growth rate became reduced. Histologically, each lobes of thymus was surrounded by a connective tissue capsule from which septa arises and incompletely divides the glands into lobules. During the day-1(D₁) period the lobules were demarcated into cortex and medulla, which becomes larger with age and well demarcated.