MORPHOGENESIS OF THE FOLLICLES 435 



iniiUHl. 15(H';uis(^ the iiuitei'iul at hand is not sufficient to war- 

 rant th(^ (h-aAving of any conclusions in tliis matter, it is not 

 listed with the materials nor discussed in this paper. 



In tVnir of the fetuses studied (Nos. 40, 42, 43, and 44) a 

 number of cyst-hke follicles located in all cases in the lower and 

 posterior (dorsal) part of the lateral lobe, were observed. Some 

 of these follicles measure as nuich as 200 microns in diameter. 

 The size of these structures is not much greater than that of some 

 of the larger normally appearing follicles. But in structure they 

 are quite different, ha\'ing walls made up of very much flattened 

 epithelial cells, whose nuclei cause the cells to bulge and are 

 separated from one another by much greater distances than is 

 the case with the nuclei in the more usual follicles. The lumina 

 of these cysts are quite regularly circular in outline and in many 

 cases contain a granular substance. It is as though a follicle 

 had been greatly distended, the cells of the wall being stretched 

 and flattened. 



Fig. 11 Model (reconstructed bj- Bern's wax-plate method) of the left lat- 

 eral lobe of the thyroid gland from a hmiian fetus 22 mm. long (No. 18). Antero- 

 lateral surface view to show the perforated (fenestrated) plates, which present 

 a relatively smooth surface. Line a-h indicates the level of the section sliown in 

 figure 1, and the level at which the model was divided to show the relations 

 pictured in figure 12. The carotid arteries are shown on the right hand side of 

 the figure. X 150. 



Fig. 12 The lower section of the model pictured in figure 11. The upper 

 portion has been removed in order to demonstrate the relations to the gland 

 mass of the appearances found in cross section. The separation of the two 

 portions is made at the level of the section shown in figure 1 and indicated {a-h) 

 in figure 11. X 150. 



Fig. 13 Model (reconstructed by Born's wax-plate method) of the upper 

 portion of the left lateral lobe of the thyroid gland from a human fetus 30 mm. 

 long (No. 30). Plates are more broken up than in figure 11 and present surfaces 

 which are relatively rough and irregular. The upper parathyroid (P.) is shown. 

 Lateral view. X 100. 



Fig. 14 Model (reconstructed by Born's wax-plate method) of a part of a 

 plate from the thyroid gland of a human fetus 30 mm. long (No. 30) at a higher 

 magnification, to demonstrate more exactly than shown in figure 13 the appear- 

 ance and relations of the mounds forming on the surface of the plate. The 

 plane a-h indicates the position of the section shown in figure 3. Lateral view. 

 X 265. 



