XI.—Upon the Thyroid Glands in the Cetacea, with Observations on the Relations of the Thymus to the Thyroid in these and certain other Mammals

Extract

In the writings of comparative anatomists, considerable difference of opinion is expressed respecting the position and relations of the thyroid gland in the Cetacea, and some authorities even have asserted that it does not exist in these Mammalia.

John Hunter states that he has examined several porpoises, balænæ, and other cetacea, yet “could not observe anything like a thyroid gland.”

Meckel believed that he found, in a fœtal porpoise (D. phocœna), eight inches long, a thyroid gland. He describes it as half an inch broad, two lines thick and high, and of equal depth and thickness both on the middle and sides of the air-tube, in the same position as that in which the gland is found in other mammals. From this examination, however, of so young a fœtus, he does not feel disposed to affirm that, contrary to the opinion of Hunter, it exists in full grown cetacea. In a subsequent paper he mentions incidentally, that in the dolphins the gland is formed of two quite separate lobes. Cuvier states that he has found the gland very distinct in many dolphins and porpoises. In these animals it was divided into two parts, and suspended from the trachea opposite the upper border of the sternum, and some distance from the larynx. Carus describes the gland in the dolphin and porpoise as consisting of two parts, entirely separate from each other. It is difficult to say, however, from the text, whether he is giving the result of his own observations, or simply adopting those of Cuvier. Dr Martyn repeats the statement that the cetacea do not possess a thyroid, and he ascribes the supposed absence of the voice in these animals to the want of this glandular structure.