Abstract
Summary The postnatal development of the ultimobranchial body in control and methylthiouracil treated Wistar rats was examined by light microscopy. Single large follicles filled with a homogenous PAS positive material and covered with a double layer of epithelial cells were observed in many thyroid glands of suckling animals. These large follicles, which are considered to be precursors of the ultimobranchial follicles and cysts in adult animals, were situated near the perivascular connective tissue and usually contained single desquamated cells in their lumen. In all control animals, killed between the 30th and 365th day of age, mature ultimobranchial follicles and cysts were noted. Tubes, rods and groups of squamous cells were also observed. A reduction in the number of ultimobranchial follicles and cysts was found in all animals treated for a long time with methylthiouracil. No difference in the number, size and structure of the ultimobranchial follicles was observed between the control and methylthiouracil treated suckling rats. The development of ultimobranchial squamous cell structures in the control and methylthiouracil treated animals has been discussed.
Published Version
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