. The endocrine organs; an introduction to the study of internal secretion . ealing not with a parathyroidbut with an accessory thyroid. The parathyroids usually remain unaltered in myxoedema :Forsyth has, however, described one case which was an exception to this rule (Trans. , 1907). Biedl has also recorded the development of colloid-containing vesicles in theparathyroid in a case of atrophy of the thyroid in man. Development of Parathyroids 21 itself take on a similar appearance, becoming large and irregular (fig. 16).In this case there is also seen a multiplication of intervesicu
. The endocrine organs; an introduction to the study of internal secretion . ealing not with a parathyroidbut with an accessory thyroid. The parathyroids usually remain unaltered in myxoedema :Forsyth has, however, described one case which was an exception to this rule (Trans. , 1907). Biedl has also recorded the development of colloid-containing vesicles in theparathyroid in a case of atrophy of the thyroid in man. Development of Parathyroids 21 itself take on a similar appearance, becoming large and irregular (fig. 16).In this case there is also seen a multiplication of intervesicular cells, whichthe authors believe to be of the same nature as the cells of the conclusion they arrive at is that the tissues of the two organs arelargely intermixed, at least in birds and mammals. In lower Vertebrates,however, Mrs Thompson found the two to be completely separate bothdevelopmentally and structurally. The parathyroids are amongst the most vascular organs in the are supplied each by a special branch of the inferior thyroid artery. ves. \-i . FIG. 16.—Section of thyroid of dog, thirty-two days after removal of all the para-thyroids. (Halpenny and Thompson.) The appearance is singularly like that ofthe parathyroid shown in fig. 15, and somewhat resembles the thyroid of ex-ophthalmic goitre (tig. 26). ves., vesicle ; , epithelium lining vesicle; , intervesicular tissue ; , connective tissue. The sinus-like capillaries come into close relationship with the epithelialcells of the gland. The nerves of the parathyroids, like those of the thyroids, pass bothto the vessels and to the secreting cells. Some evidence has been adducedwhich seems to show that the cell-activity is controlled by the nervoussystem. Development.—The parathyroids are developed as outgrowths of theIllrd and IVth visceral pouches on each side (fig. 2), that from theIllrd pouch giving rise to the upper, and that from the IVth to the lowerpar
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