II. The thyroid and parathyroid glands throughout vertebrates, with observations on some other closely related structures

Abstract

The main object of the investigation, the results of which are given in the present communication, is to throw light on the question as to a morphological and functional relationship between the thyroid and parathyroid glands. Incidentally it has been necessary to describe the appearances and discuss the significance of some closely allied structures, that is to say, of other tissues and bodies which are developed in the region of the mucous membrane of the fore part of the alimentary tract, such as the post-branchial body, the ventral “ Kiemenrest ” of anura, the carotid body, and pars intermedia of the pituitary. A large amount of work has been done upon the development of the parathyroids, thymus, and some of the less known gill cleft derivatives (especially in the lower vertebrata) such as the ventral branchial bodies in anura, and the doubtful structure known as the carotid gland. On the other hand, detailed descriptions in the adult condition accompanied by illustrations are wanting, or at any rate inaccessible. Thus, even such detailed accounts of the branchial organs as are given by Gaupp are unaccompanied by drawings, and I am not aware of the existence of a histological illustration of the ventral branchial body in the Frog, one of the most striking organs of the cervical region of the animal, larger than thyroids and parathyroids together, and in my experience, indeed, the only one of the series which can be readily found by the ordinary methods of dissection. For these reasons it seemed that a series of drawings of these bodies in the lower vertebrates would be valuable.