. Anatomy, descriptive and applied. Anatomy. 1440 THE DVCrLESS GLANDS Structure.—The structure of the parathyroids is different frora that of the thyroid. They are composed of groups of epithehal ceils arranged in a chain-Iilie fasliion with numerous inter- vening capillaries. There is a certain type of cell, but the form varies. These variations result from changes due to episodes of rest and activity (Verebely). MacCallum's studies seem to lead to the same conclusion. Thomson' states that he finds only one type of cell in the infant gland, and that in the adult there is primarily but one typ
. Anatomy, descriptive and applied. Anatomy. 1440 THE DVCrLESS GLANDS Structure.—The structure of the parathyroids is different frora that of the thyroid. They are composed of groups of epithehal ceils arranged in a chain-Iilie fasliion with numerous inter- vening capillaries. There is a certain type of cell, but the form varies. These variations result from changes due to episodes of rest and activity (Verebely). MacCallum's studies seem to lead to the same conclusion. Thomson' states that he finds only one type of cell in the infant gland, and that in the adult there is primarily but one type of cell, the other cells noted being modifications of the principal cell due to degeneration or hyperfunction. There is much lym- phoid tissue in the interstitial connective tissue. The capillaries are of the sinusoidal variety. The nerves of the parathyroids are derived from the sympathetic system. Each parathyroid gland is supplied by a parathyroid artery. The inferior parathyroid artery is always a branch of the inferior thyroid artery or of the anastomosing channel between the superior and inferior thyroid arteries of one side (Geist). The superior parathyroid artery may be a branch of the superior thyroid (Poole), but it is usually a branch of the inferior thyroid or of the anasto- mosing channel. Ginsburg' has shown that each of the glands has an accessory blood supply, by anastomotic channels from the opposite side. Embryology.—The parathyroids develop chronologically in advance of the thyroid. They are derived from the third and fourth branchial clefts of each side. An independent accessory parathyroid may develop from the fifth cleft (Getzowa, Michand). Some have regarded the para- thyroids as embryonic portions of the thyroid, but, as MacCallum says, " there is no histological proof that parathyroid tissue can ever become converted into thyroid ; Most observers regard the parathyroids as distinct glands possessed of a special function. Certain i
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1913
