The parathyroid glands of the Mongolian gerbil (Meriones unguiculatus).

The parathyroid glands of adult Mongolian gerbils were studied under an operation microscope, as well as with the aid of conventional light microscopy, and transmission and scanning electron microscopy. The mean serum level of calcium was 5.1 mEq/1 and that of phosphorus was 4.8 mg/100 ml. The animals possessed two small parathyroid glands, usually situated anteriorly and slightly laterally to the superior thyroid poles. The glands had a rich vascular supply and were composed of sheets of chief cells, which varied in electron density and content of organelles. No water-clear, oxyphil, or intraglandular fat cells were found. Some mitochondria exhibited electron lucent areas, and separation and bulbous projections of the membranes. The cell membranes were straight or tortuous and possessed microvilli, occasionally with central filamentous structures. The intercellular spaces were usually narrow. It is supposed that the variants of chief cells are interchangeable and that the differences in their morphological appearance are related to differences in functional state.