THE PARATHYROID BODIES. 



199 



common and contain materials of a mucous or fatty nature. Large granular ele- 

 ments, interstitial cells, occur within the connective tissue between the follicles. 

 The blood-vessels supplying the thyroid tissue are unusually plentiful, 

 the interlobular arteries, branches from the superior and inferior thyroids, 

 breaking up into close networks that surround the follicles and lie imme- 

 diately beneath the epithelium. The lymphatics, also abundant, begin as 

 perifollicular lymph-spaces, from which are formed the interlobular lym- 

 phatics accompanying the blood-vessels. The deeper lymphatics join the 

 superficial plexus, on the surface of the organ, from which the larger trunks 



/-Follicle 



- Interlobular vessels 



Capillary network 



surrounding 



follicle 



Follicle containing 

 colloid 



FIG. 247. Section of injected body, showing rich capillary networks surrounding follicles. X 46. 



pass in different directions. The nerves are, for the most part, sympathetic 

 fibres supplying the walls of the blood-vessels and enclosing the follicles in 

 plexuses of nonmedullated filaments, which end in close relation with the 

 epithelial cells. 



THE PARATHYROID BODIES. 



These little organs, also called the epithelial bodies, when typically 

 present are arranged as two pairs, an upper and a lower. The upper ones 

 are the more constant and usually lie against the posterior surface of the 

 lateral thyroid lobes. The inferior bodies are less constant, both as to 

 position and presence, sometimes lying against the side of the trachea under 

 cover of the lower part of the thyroid lobes, or upon the latter, and at other 

 times being placed entirely below the thyroid. The disposition of the para- 

 thyroids may be asymmetrical, in some cases as many as four, in others none, 

 lying on one side. The bodies are 6-7 mm. long, 3-4 mm. broad, and 1.5-2 

 mm. thick, but may be larger or smaller. They arise from the dorsal wall 

 of the third and fourth pharyngeal furrows and thus differ from the thyroid 

 body in origin, as well as structure. 



Each organ is invested by a thin fibro-elastic capsule and subdivided 

 into uncertain lobules by delicate sept?, which support the larger blood- 



