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PARATHYROID

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Originally appearing in Volume V08, Page 635 of the 1911 Encyclopedia Britannica.
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PARATHYROID GLANDS These little See also:

oval bodies, of considerable physiological importance, are two in number on each See also:side. From their position they are spoken of as postero-See also:superior and antero-inferior; the postero-superior are embedded in the See also:thyroid at the level of the See also:lower border of the cricoid See also:cartilage, while the antero-inferior may be embedded in the lower edge of the lateral lobes of the thyroid or may be found a little distance below in relation to the inferior thyroid See also:veins. They are often very difficult to find, but it is easiest to do so in a perfectly fresh, full-See also:term foetus or See also:young See also:child. Microscopically they consist of solid masses of epithelioid cells with numerous See also:blood-vessels between, while, embedded in their periphery, are often found masses of thymic See also:tissue including the concentric corpuscles of Hassall. They have been regarded as undeveloped portions of thyroid tissue in an embryonic See also:state, but the experiments of Gley (Comptes rendus de la See also:Soc. de Biol. No. I1, 1895) and of W. See also:Edmunds (Prot. Physiol. Soc.-Journ. Phys. vol. xviii., 1895) do not confirm this. They are See also:developed from the entoderm of the third and See also:fourth branchial grooves.

Parathyroids have been found in the orders of See also:

Primates, Cheiroptera, See also:Carnivora, See also:Ungulata and See also:Rodentia among the See also:Mammalia, and also in Birds. In the other classes of vertebrates little is known of them. The fullest and most See also:recent See also:account of these bodies is that of D. A. Welsh in Journ. Anat. and Phys. vol. 32, 1898, pp. 292 and 380.

End of Article: PARATHYROID

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