author(s)
K Rajalakshmi, Geetha Ramesh, Usha Kumari, M Sivakumar, S Uma and Lakkawar AW

abstract
A study on the histomorphology and histochemistry of the parathyroid glands was conducted in the prenatal and postnatal age groups of sheep. For the prenatal study, the thyroid gland was collected from sheep embryos of early (42 days), mid (77.7 days) and late (128 days) gestation. Postnatal study included the collection of external parathyroid glands from young (<1 year), adult (1-5 years) and old (> 5 years) sheep, irrespective of the sexes. Tissue pieces were collected in different fixatives for routine paraffin embedding. Paraffin sections were used for routine and special staining techniques. Frozen sections were used for histochemical techniques. The internal parathyroid gland in the early, mid and late gestation embryos was observed within the section of the thyroid gland on the dorso-medial aspect. The general architecture of the parenchyma of the internal parathyroid in the prenatal age groups was similar to the postnatal age groups studied. In the postnatal age groups, the parathyroid gland was surrounded by a connective tissue capsule. From the capsule, thin indistinct trabeculae extended into the parenchyma, but did not form any compartments. The parenchyma of the internal and external parathyroids in all the age groups consisted of the light and dark chief cells. C cells were noticed in the internal parathyroids, but were absent in the external parathyroids. Three types of follicles namely, light, dark and mixed follicles were observed in the young and adult age groups. Older animals showed only light follicles. Some of the light follicles contained colloid in their lumen. The colloid in the light follicles of the internal and external parathyroids in all the age groups was PAS positive. The presence of lipids, acid and alkaline phospahatases were recorded in the parathyroid gland.