168 Herring 



cells in its wall. The pouch is widening out behind the neck, and the latter 

 is found to be constricted when the sections next in series to it are examined. 

 The anterior wall of Rathke's pouch is closely applied to the wall of the 

 cerebral vesicle, and at the dorsal extremity of the pouch an invagination 

 of the wall of the cerebral vesicle is forming the primitive infundibulum. 



The head of the notochord bears no immediate relation to Rathke's 

 pouch, and is separated from it by a clump of cells which is continuous with 

 the epithelium of the fore-gut, and appears to be formed by a proliferation 

 of the cells of the latter. A large blood-vessel (c) is also seen in this 

 specimen, lying between Rathke's pouch and the head of the notochord. 



At this stage it is difficult to determine where ectoderm ends and 

 entoderm begins ; the upper stump of the oral plate has disappeared as such, 

 and its representative is uncertain. There is no indication of a pouch in 

 the fore-gut, but the clump of cells appears to be derived from the wall of 

 the latter. Minot (22) makes the fold of epithelium at the posterior 

 margin of Rathke's pouch homologous with the upper lip of Petromyzon. 

 If this is the case, the fore-gut must begin behind this fold. The close 

 relation between the head of the notochord and the cell clump makes it 

 likely that the latter is derived from the fore-gut, for, in the 4-mm. embryo, 

 the head of the notochord is some distance behind the oral plate, and the 

 epithelium opposite it is that of the fore-gut. The clump of cells is the 

 only structure which resembles the proliferation of entoderm described by 

 Kupf f er. It is not found in any of tlie older embryos that I have examined, 

 but the amount of suitable material at disposal for this purpose has been 

 limited. Rathke's pouch is the only part that enters into the formation of 

 the anterior lobe of the pituitary ; it is single and median in origin, and 

 there is no indication in the embryos of the cat and the pig of any other 

 " Anlage " for the anterior lobe. I have not found any communication 

 between the epithelium of Rathke's pouch and that derived from the fore- 

 gut, as described by Nusbaum in the dog, but cannot say that this does 

 not occur. In the specimens I have examined there is nothing to indicate 

 in the slightest degree that Rathke's pouch is reinforced by epithelium 

 from the fore-gut. The epithelial proliferation of the latter disappears as 

 stated by Kupff er, and takes no part in the formation of the pituitary. 



One of the most important characteristics of the developing pituitary is 

 the close union maintained between buccal and cerebral portions from the 

 earliest stage. Minot (22) emphasised its importance in mechanically 

 keeping the two parts together, and thus explaining their intimate relations. 

 Salzer (33) also noted it, and states that he could find no connective tissue 

 between the infundibular process and hypophysial sac. With these obser- 

 vations I thoroughly agree. The buccal epithelium in the anterior part of 

 the hypophysial angle is intimately connected with the epithelium of the 

 cerebral vesicle, without the interposition of connective tissue. In the 

 further growth of the embr^'o this close union is preserved, but in other 

 parts connective tissue develops and separates the buccal epithelium from 



