author(s)
GSS Chandana and K Balasundaram

abstract
The primordium for thyroid gland in sheep fetuses was observed by 24 days of gestation at the floor of the pharynx. By 44 days of gestation, the gland showed presence of clumps of basophilic cells. It was surrounded by delicate connective tissue capsule whose thickness increased with gestational age. By 51 days of gestation, the clumps of cells were arranged to form curved cords. By 57 days of gestation, cells were organised into numerous follicles of different sizes filled with colloid. By 65 days of gestation, parafollicular cells were observed in between follicles. By 106 days of age vacuoles were noticed in periphery of the colloid in some follicles.