456 THE DUCTLESS GLANDS 



thyroid bodies have been frequently confused. They are also 

 much less vascular than the parathyroids. 



III. THE PAKATHYROID GLANDS 



The parathyroids are small glandular bodies of irregular distri- 

 bution, usually found in relation with the posterior margin of the 

 lateral lobes of the thyroid gland. Frequently they occur in rela- 

 tion with the tracheal or laryngeal wall and may be found as high 



Fie. 361. TRANSECTION or A PARATHYROID GLAND OF MAN. 

 Heinatein and eosin. Photo, x 10, 



as the hyoid bone or as low as the border of the thymus. In man 

 they are asymmetrical in their distribution, no more than two being 

 present on either side. They also vary greatly in size and shape, 

 but usually -are of ovoid form and about 3 to 5 mm. in diameter. 



Each parathyroid is invested by a thin capsule of dense con- 

 nective tissue and consists of a mass of epithelial cells supported 

 by a delicate fibrous reticulum. The epithelial cells are of two 

 chief types, designated by Welsh* as the "principal" and the 

 " oxyphile " or acidophile cells. 



The principal cells are the more abundant. They are ovoid or 

 spheroidal elements, with a clear vesicular cytoplasm, a distinct 

 cell membrane, and a large spherical nucleus, whose chromatin is 

 irregularly distributed and often gives the nucleus, a somewhat 

 vesicular character. 



* J. Anat. and Physiol., 1898. 



