HISTOLOGY OF THE HYPOPHYSIS CEEEBEI Til 



parathyroids in possessing a high growth energy. In congenital hypo- 

 plasia the anterior lobe is most affected. 



We have no data for man on the time of maturity of the hypophysis. 

 Lewis(c) has found that in pig fetuses between 125 and 175 millimeters in 

 length "the secretion of the pars intermedia becomes as active as that of 

 the adult gland." At birth the fetuses measure about 280 millimeters, 

 and Lewis estimates that fetuses of 125 millimeters are "about nine and 

 one half or ten weeks old from conception." As yet, we have no informa- 

 tion relative to the anatomical changes coincident with the appearance of 

 secretory activity in mammals. 



Early Endocrin Function of the Hypophysis. Smith's(&) observa- 

 tions on the anterior lobe of the hypophysis in young tadpoles have shown 

 that, in these very early stages, this part of the hypophysis supplies a sub- 

 stance or substances having a specific action on growth and pigmentation. 

 The fact that the secretions are thrown out before acidophilic and basophilic 

 granules and other evidences of cell differentiation make their appear- 

 ance, supports the conclusion (in the parathyroid section) that the 

 optically homogeneous ground substance is the formative agent, and that 

 the absence of visible secretion antecedents means but little. And further- 

 more, since we have no reason to believe that the adult hypophysis pro- 

 duces a substance which plays a part in pigment formation, we must con- 

 clude that its production, like that of so many other products of the 

 endocrin organs, is restricted to very young animals. This brings up the 

 point that we must not expect the extracts of the ductless glands of adult 

 animals, when used in feeding experiments, invariably to possess the same 

 physiologically active substances as those of young animals. 



Comparative Anatomy 



The hypophysis is a very ancient organ, which is represented in all 

 classes of vertebrates. In the myxinoidea it discharges directly into the 

 pharynx. In attempting to establish homologies in the vertebrate scale, 

 Worderman's work may be used as a guide. It is possible that we may 

 be dealing with a succession of glandular organs, or of the responses of 

 fundamentally similar organs to very different conditions. Certain it is 

 that the size of the hypophyseal complex, relative to the brain as a whole, 

 decreases very noticeably as we pass upward in the phylogenetic series. 

 From a practical point of view, in mammals there are two chief variables, 

 the extension of the cavity of the third ventricle into the posterior lobe, 

 and the investment of the posterior lobe by the pars intermedia. 



In man and most other mammals the posterior lobe is solid, but in the 

 cat the pars nervosa is hollow and communicates freely through the m- 

 fundibulum with the ventricle. For experimental purposes it is possible 



