Chemical and physiological studies of the parathyroid hormone.

The parathyroid glands have been recognized in all classes of vertebrates with the exception of fishes (1). As a rule there are four distinct glands so situated with regard to the thyroid gland that they have been referred to as the superior or external and the inferior or internal pairs. Sandstrom (2) was the first to describe the superior pair. For some reason or other they were forgotten until eleven years later - 1891 - they were rediscovered by Gley (3). The inferior pair were described by Kohn (4) in 1895. Accessory parathyroid tissue is sometimes present and may be situated in the thorax nearer to or embedded in the thymus gland (1). The parathyroids develop as thickenings of the endoderm of the third and the fourth branchial clefts. The superior pair of glandules is related to the fourth branchial clefts with reference to development while the inferior pair is similarly related to the third branchial clefts. [...