CHAPTER XXI 



THE THYREOID AND PARATHYREOID, THE PITUITARY 

 BODY, THE PARAGANGLIA AND THE ADRENAL. 



The Thyreoid 



The thyreoid (Fig. 288) is a ductless structure built upon the 

 general principle of a compound alveolar gland. There are usually 

 two lateral lobes connected by a narrow band of glandular tissue, 

 the "isthmus." Each lobe is surrounded by a connective-tissue 

 capsule, from which septa pass into the lobe, subdividing it into 





Fig. 28S. — Section of Human Thyreoid. Most of the alveoli contain colloid. 



lobules. From the perilobular connective tissue finer strands extend 

 into the lobules, separating the alveoli. The latter are spherical, 

 oval, or irregular in shape. They vary greatly in diameter (40 to 

 i2o«) and are as a rule non-communicating. At birth most of the 

 alveoli are empty, but soon become more or less filled with a peculiar 

 substance known as "colloid." The alveoli are lined with a single 



40s 



