An Analysis of the Juxta-Neural Epithelial Portion etc. 28l 



its ultimate conflguration; it is possible to define the eminentiae 

 laterales ' and the eminentia saccularis, which latter is now almost 

 complete]}' surrounded by the fused tuberai processes. 



70 mm Cat Embryo no. 478 (plate VII, figs. 5 and 6). 



The neural and glandular elements have in this stage attained 

 their ultimate arrangement and relations. The caudal horns of the 

 tuberai processes have met across the median line caudad of the in- 

 fundibulum, and have fused. In this way the pars tuberalis has 

 taken on its adult form and position. The eminentia saccularis of 

 the tuber cinereum now rests in the pars tuberalis, while the latter 

 forms a complete investment of the ventro-cephalic and caudal sur- 

 faces of the saccular eminence except for the small hiatus through 

 which the infundibulum passes ventrad to become the expanded in- 

 fundibular process. As a result of assuming this juxta-neural position, 

 the pars tuberalis has forced the original dorsal surface of the buccal 

 sac completely away from contact with the brain. The pars infundi- 

 bularis invests the infundibulum and infundibular process so that it 

 occupies the juxta-neural position with reference to these neural ele- 

 ments. There remains a portion of the glandular tissue which has 

 no such close relation to the brain, the pars distalis; it is, in fact, 

 separated from the infundibulum and infundibular process not only 

 b\' the pars infundibularis but also by the wide residual lumen. 

 Interposed between it and the saccular eminence is the pars tuberalis. 



These facts make it possible to state that the juxta-neural portion 

 of the hypophysis arises from the combination of two genetically 

 distinct elements, the pars tuberalis and the pars infundibularis. 



The pars infundibularis has its origin in the caudal extremity 

 of the buccal sac and the two caudal projections from it. This forms 

 a complete investment of the infundibulum and infundibular process. 

 It is juxta-neural from the earliest stages. The pars tuberalis arises 

 as two lateral processes which subsequently fuse with each other 

 across the median line and secondarily acquire a juxta-neural position 

 by investing the eminentia saccularis. 



The phases in the development of the neural portion of the hypo- 

 physis are shown in text figures 3 to 10 inclusive, which represent 



