HYPOPHYSIS CEREBRI 309 



cells which, under normal conditions, largely predominate. The 

 actual number of the eosinophile cells remains unchanged, but 

 they are noticeably reduced in size. The basophile cells are 

 entirely unaffected, the whole of the pregnancy changes taking 

 place within the principal cells. These practically cease to exist 

 as such, being almost entirely transformed into pregnancy cells. 

 The pregnancy cells have large, light, irregular nuclei, with 

 abundant plasm which is distinctly granular and stains red with 

 eosin. They accumulate in large numbers in the two lateral por- 

 tions of the hypophysis; in the posterior portion, where the 

 eosinophile cells are ranged in compact masses, they are scanty I 

 but not entirely absent. The pregnancy cells are grouped in 

 broad columns and in alveoli, generally occupying the centre of 

 the alveolus. Occasionally, when pregnancy is at its height, 

 these cells form agglomerations which suggest adenomatous 

 hyperplasia. After parturition, involution of the pregnancy cells 

 takes place and they largely reassume their former appearance 

 of principal cells. There is, however, an increase in the number 

 of the principal cells now present, and at the next pregnancy 

 these undergo changes similar to the last, so that the result, 

 though qualitatively the same as at the first pregnancy, is quanti- 

 tatively very much more intense. 



In the hinder boundary layer of the anterior lobe (Pere- 

 meschko's medullary layer, Thaon's region interglobulaire), a 

 fissure is frequently, though not invariably, observed in the 

 neighbourhood of the hilus ; it is lined with a single layer of 

 cubical cells or, more rarely, ciliated columnar cells, and its 

 hollow is either empty, or contains a substance which stains pale 

 blue with hcematoxylin. This fissure represents the embryonal 

 hypophysal cavity. Two kinds of vesicles or follicles are also 

 observed in this region. By the side of the fissure, and sometimes 

 in place of it, rounded vesicles are occasionally seen, which are 

 lined with columnar epithelium and filled with an amorphous 

 mass ; they are probably formed from depressions in the posterior 

 wall of the embryonal hypophysal cavity. A second variety of 

 vesicles, found in the same neighbourhood, is considerably larger ; 

 both in appearance and in their colloid reactions, these vesicles 

 are reminiscent of the follicles of the thyroid. The vesicle wall 

 is composed of cubical cells, which do not stain readily and con- 

 tain large nuclei ; the lumen of the vesicle is sometimes filled with 

 an amorphous homogeneous mass. In^addition to a finely granu- 

 lar basophile substance, an eosinophile substance resembling the 

 colloid of the thyroid is sometimes seen. Vesicles of this descrip- 

 tion are usually encountered in the posterior medullary layer, and 

 occasionally also in the interior of the anterior lobe. 



By means of Golgi's method, Gentes and Pirrone discovered 

 nervous elements in the walls of these vesicles, similar to those in 

 the sensory cells of the olfactory region of the nasal mucous 

 membrane. 



