The accessory thyroid glands of the dog around the intrapericardial aorta.

Abstract

The accessory thyroid glands distributed in the fatty tissues surrounding the ascending aorta of the dog were investigated by light and electron microscopy.1. Out of the 45 dogs examined, 29 possessed one or more accessory thyroid glands, in the most numerous case six (Table 1). They were generally oval in form and measured 1-2mm in long diameter.2. There was recognized not a single parafollicular cell in the accessory thyroids, although 26 glands were examined in serial sections and stained by silver impregnation, pseudoisocyanin and lead-hematoxylin known as the positive staining methods for the parafollicular cells. Otherwise, the light and electron microscopic structures of the accessory thyroids corresponded to those of the main thyroid glands.3. The reactions under the light and electron microscopes of the follicular cells of the accessory thyroid to hypophysectomy and treatment of antithyroid drug were identical with those of the main thyroids.4. After thyroidectomy, the accessory thyroids showed conspicuous hyperactivity. Although their morphological changes resembled those of the animals injected with antithyroid drug, they scarcely proliferated.5. In dogs with induced hypercalcemia the accessory thyroid glands were not affected at all.6. The present study indicates that the follicular cells and parafollicular cells were of distinct cell lines and that the accessory thyroid glands may be separated from the main thyroid before the latter incorporates the ultimobranchial body.