An Analysis of the Juxta-Neural Epithelial Portion etc. 283 



active as late as the 17 mm embryo. Subsequently this cephalic 

 projection becomes less marked and in the 25 mm stage is indicated 

 only by a slight thickening- in the cephalic extremity of the infun- 

 dibular process. In all later stages the lines of growth are confined 

 to the ventral and caudal surfaces. The saccular eminence reaches 

 its greatest devolopment in the 70 mm stage where it appears as a 

 well defined medial protuberance of the tuber cinereum. Its ventro- 

 cephalic surface presents a long horizontal portion rising from which 

 to the region immediatel}^ behind the chiasm is a short vertical 

 portion of this surface. The caudal surface of the saccular eminence 

 is relatively small while from the junction of the ventro-cephalic and 

 caudal surfaces the infundibulum projects ventrad to terminate in the 

 expanded infundibular process. The ventricular cavities contained 

 within these parts are relatively small. The recessus tuberis has 

 attained its adult relations and configuration. It is in general some- 

 what more emphasized than in the adult due to the fact that the 

 post-chiasmatic process is more prominent in this stage than later. 

 The recessus infundibuli is a small tubular channel which expands at 

 its caudal extremity into the extensive recessus processi infundibuli. 



Ontogenesis of the Pars Tuberalis in the Chick. 

 Chick of 4 days. Embryo no. 185 (plate XV, fig. 23). In this 

 stage the anläge of the pituitary gland has already made its appe- 

 arance as a large evagination from the dorso-caudal portion of the 

 mouth cavity \_26\ This is Rathke's Pocket; it has attained a juxta- 

 neural position throughout its entire extent. Ventral to this evagi- 

 nation is a second pouch which has its axis parallel to Rathke's 

 Pocket [2o\. It has no relation to the floor of the diencephalon and 

 is usually accounted an entodermal derivitive under the term of 

 Seessel's Diverticulum [Sï\. Only a small area of entoderm intervenes 

 between the cavity of these two pouches, so that there is ample 

 opportunity for some of the entodermal elements of Seessel's Pouch 

 to become included in the pituitary evagination by a process of epi- 

 bole. This question requires a more extended study of the cyto- 

 genesis in the region involved. The floor of the diencephalon [27] 



