HISTOLOGY OF THE HYPOPHYSIS CEREBKI 709 



into contact with the infundibular process, which is a downgrowth from 

 the floor of the third ventricle, and which ultimately forms the pos- 

 terior lobe. For convenience of description, we may divide Rathke's 

 pouch into three parts, cranial, intermediate and pharyngeal. 



Structures from the Cranial Portion of Rathkes Pouch (Pars An- 

 terior Propria, Pars Intermedia, and Pars Tuberalis). The cranial por- 

 tion of Rathke's pouch usually becomes completely separated from the 

 pharynx by the growth of the base of the skull and the formation of the 

 sella turcica. A good account of the histogenesis is given by Tilne} 

 from whom I quote. In an embryo of twenty millimeters Rathke's pouch 

 is in the form of a closed sac, somewhat flattened anteroposteriorly. 



The anterior wall is destined to give rise to the anterior lobe proper ; 

 the lumen of the cleft often persists in the adult hypophysis, and the 

 posterior wall develops into the pars intermedia. The cells constituting 

 the anterior wall multiply rather more rapidly than those in the pos- 

 terior wall, and become arranged in cords which are very noticeable 

 in a twelve weeks 7 fetus. During the fifteenth week the cell cords become 

 for the most part rearranged into acinus-like clumps. At this stage, the 

 cells are all of the basophilic variety. There are indications that cells 

 of the posterior wall penetrate into the neighboring infundibular process. 

 Connective tissue elements from the diaphragma sellse migrate into the 

 interior of the gland. The posterior or intermediate portion begins to 

 extend upward along the infundibular stalk, and probably gives rise to 

 the tissue which has been recently called the pars tuberalis (Tilney(a)). 

 In a human fetus of eight months the anterior and intermediate lobes are 

 characterized by their extreme vascularity and by the deposition of col- 

 loid material in the cleft. Acidophilic cells make their first appearance 

 during the ninth month of development. Their origin is not clear. The 

 regional distribution of the various cell types will be discussed later 

 (p. 714). 



Accessory Hypophysis. Occasionally the cranial anlage splits up at an 

 early stage, with the result that small accessory glands develop, which, 

 like the parent gland, are usually confined to the sella turcica. These ac- 

 cessory glands, when formed, are often fully differentiated and must be 

 regarded as potential sources of internal secretion. The parahypophysis, 

 described by Dandy and Goetsch in dogs, belongs in this category. 



Little clusters of squamous epithelial cells have been found in the 

 hypophysis by both Erdheim and Lewis, which have a marked tendency to 

 tumor formation. Lewis remarks upon the fact that these misplaced 

 fragments of buccal epithelium usually occur in the infundibulum and 

 the adjacent portion of the anterior lobe. 



Structures from the Intermediate Portion of Rathke's Pouch (Canalis 

 Craniopharyngeus). While the intermediate portion of the pouch usually 

 disappears completely with the development and ossification of the 



