328 



M. JACKSON 



it is evident that the portions described by Tihiey ('13) in the 

 floor of the third ventricle (eminentia saccularis and pars tuber- 

 aUs) are not included in the parts examined. 



From table 2 A it is evident that dming normal postnatal 

 growth there is considerable individual variation in the relative 

 size of the various lobes. On comparing the younger (newborn 

 to three weeks) with the older rats (ten weeks and above), how- 



Fig. 1 From photographs representing frontal (coronal) sections through the 

 normal hypophysis of the albino rat (A) at three weeks (rat J 1.2) and (B) at 

 ten weeks (St 47.5). The hypophyseal cavity (residual lumen) and the three 

 parts (anterior, intermedia and nervosa) are apparent. The anterior lobe is 

 relatively larger in the older rat. X 25. 



ever, it appears that in general the pars anterior becomes rela- 

 tively larger, the pars nervosa correspondingly smaller. The 

 pars intermedia is variable, but in general apparently undergoes 

 no definite change in relative size in either direction. 



That the hypophysis is relatively heavier in the female rat is 

 already known (Hatai '13). The present data indicate that this 

 is due chiefly, if not entirely, to a larger anterior lobe in the 

 female. Comparing the 4 older males in table 2 A with the 4 

 corresponding females, we find the following averages: 



