THE THYROID GLAND. 



The Thyroid Gland. 



107 



At an early embryonic period this gland opens into the 

 pharynx by an outlet-duct ; but this soon disappears, leaving 

 the alveoli isolated and ductless. 



The sustentacular connective tissue of the gland consists of 

 a firm fibrous capsule enveloping the organ ; trabeculce or septa 

 (interlobular), of similar fibrous tissue, which divide the gland 

 into lobes and lobules ; and a delicate inter alveolar or intra- 

 lobular tissue between and supporting the secretory alveoli. 



The glandular alveoli are spherical or oval saccules, without 



FIG. 44. 



Alveoli of thyroid gland (Dunham). 



outlet-ducts and entirely closed and isolated from one another 

 (Fig. 44). They are lined with a single layer of cuboidal 

 epithelium-cells with prominent nuclei. The cavities or 

 lumina within the alveoli are of considerable size, are filled 

 with secreted colloid substance, and their margins often have a 

 scalloped appearance. 



The bloodvessels of the thyroid are exceedingly ample, and 

 distribute a rich capillary network about the saccules. 



