514 A TEXTBOOK OF PHYSIOLOGY 



from the median portion (Fig. 240). The cells first form networks 

 of solid cords. These separate into solid masses, within which lumina 

 may appear. The mature gland consists of rounded closed spaces or 

 vesicles filled with a colloid material, and by a single layer of low 



e. internee. 



: --A.\ Ptafc -i 



" ?> .*.' *.! *. 



FIG. 250. THYROID OF NORMAL DOG. x 120. (Swale Vincent.) 



c., Colloid; e. ves., epithelium lining vesicles; e. interves., epithelial intervesicular 

 tissue ; c. ves., colloid vesicle. 



Fio. 251. PAKATHYEOID OF NORMAL DOG. x 120. (Swale Vincent.) 

 s.c.c., solid columns of cells; bl.v., bloodvessel. 



columnar cells (Fig. 250). The vesicles are separated by connective 

 tissue, which carries the bloodvessels and nerves, with which the 

 gland is most plenteously supplied. The parathyroids are built up of 

 closely packed polygonal cells divided up by connective-tissue septa 

 into areas of various shapes (Fig. 251). 



