CHAPTER XII. 



THE THYROID GLAND. 

 BY E. VERSON. 



THE term thyroid gland is applied to an organ composed of 

 a framework of connective tissue condensed externally to a 

 more or less thick investing membrane, and traversing the in- 

 terior of the organ in the form of strong trabeculse ; and, se- 

 condly, of gland vesicles, sustained by the framework, which, 

 as their name implies, constitute structures similar to the acini 

 of a gland, but completely closed and vesicular. 



The vesicles of the thyroid gland are composed of a thin 

 transparent hyaline membrane, lined by epithelium, the cells 

 of which are arranged in a single layer, and in fresh, uninjured 

 specimens appear longer than broad, and are provided with a 

 spheroidal nucleus, which may itself include one or several 

 nucleoli. In this condition, however, the epithelium of the 

 vesiculse is only encountered in quite young animals when 

 examined with the microscope immediately after having been 

 taken from the living animal. In a very short time, even 

 under the eye of the observer, the free surface of the cell wall 

 may be seen to project irregularly, and spheroidal tenacious 

 and hyaline drops, which after some time coalesce in the centre 

 of the vesicle, gradually develop from 'the bodies of the epi- 

 thelial cells. Usually, however, delicate lines of demarcation 

 may be recognised between them, giving a facetted appearance 

 to the clump of escaped and coalesced cell contents. Before 

 these drops become intimately fused with each other in the 

 centre they frequently indicate the path they are about to 

 pursue by pseudopodial processes which partly adhere to the 

 cell wall. These contents, at a more advanced age, and 

 under pathological conditions, are converted into colloid, though 



