588 



THE TISSUES. 



II. THE THYKOID GLAND. 



The thyroid gland consists of closed gland- vesicles g ^ to 5 i^ of 

 an inch in diameter, surrounded by a fibrous stroma, and collected 

 into rounded or polygonal lobules ? 1 S to J 4 of an inch in diameter, 

 which are associated into lobes ; and finally the latter, invested by 

 a fibrous membrane, constitute the whole organ. 



Little need be said of the fibrous tissue or stroma, since it is 

 mere common areolar tissue. Only the vesicles need a special de- 

 scription. 



The gland-vesicles present such varied conditions of structure, 

 that it is not easy to decide what is their normal state. They con- 

 sist ls, of a basement-mem- 



Fi g- 415 - brane lying on the connective 



tissue between them; 2dly, of 

 an epithelium; and, 3c%, fluid 

 contents. The basement-mem- 

 brane is T;5 J^ of an inch 

 thick, and presents no pecu- 

 liarities. The epithelium con- 



sists of a single layer of po- 

 lygonal, finely granular cells, 

 Woiy to joW of an inch in 

 diameter, with simple nuclei. 

 (Fig. 415.) The fluid con- 

 tained in the cells is clear, 

 somewhat viscous, with a tinge 



Some gland-vesicles from the thyroid gland of a ' 



child, a. Connective tissue between them. b. Mem- of yellow, and highly albu- 

 brane of the gland-vesicles, c. Their epithelium. 



(xsaa*r.) mmous. 



If, however, the organ be 



changed from its normal state, different conditions are presented. 

 Frequently no epithelium is met with, but only a fluid mixed with 

 minute granules, and free nuclei. The vesicles are also more or 

 less filled with a colloid substance in the form of transparent, amor- 

 phous, light-yellowish, soft masses. This, filling the vesicles, trans- 

 forms the latter into cysts of T J^ to ^ of an inch, in which the 

 epithelium is no longer distinct; and which, causing the stroma to 

 disappear by their pressure, ultimately coalesce into larger sinuous 

 cavities. (Fig. 416.) 



