An Analysis of the Juxta-Neural Epithelial Portion etc. 275 



These differences are shown by reconstruction based on embryonic and 

 fetal stages in the cat and common fowl. The stages selected in the 

 cat were as follows: 7 mm, 10 mm, 14 mm, 17 mm, 25 mm, 31 mm, 

 51 mm and 70 mm; those of the chick were taken at 4 days, 5 days 

 and 20 hours, 6 days and 22 hours, 10 days and 22 hours and 16 days. 

 The observations made in these studies were found to hold true of the 

 embryonic stages in the rabbit, pig and man. 



In order to follow the development of the hypophysis it was 

 necessary to note, 1. the behavior of the buccal portion through the 

 several stages and, 2. the behavior and relations of the neural portion. 



7 mm Cat embryo no. 266 (plate XIII, fig. 17). The buccal eva- 

 gination, known as Rathke's Pocket [25], has already been formed. 

 It has a wide connection with the oral cavity [26] and shows no 

 evidence of the constriction which will subsequently detach it from 

 the mouth. The pouch presents a dorsal surface, a cephalic and 

 caudal extremity. The dorsal surface is in contact with the floor of 

 the diencephalon [27] and hence is juxta-neural in position. It is 

 essential to note that this primitive juxta-neural position of the dorsal 

 surface is only transient. Its ultimate position is determined by the 

 important role which the pars tuberalis plays in the development of 

 the gland. The cephalic and caudal extremities of buccal evagination 

 are free of all contact with the brain. The floor of the diencephalon 

 has as yet made little response to the oral pouch which is now in 

 contact with it. At one point, however, there is evidence that the 

 neural portion is beginning to take form; this is seen in the region 

 of the floor of the diencephalon immediately dorsal to the caudal 

 extremity of Rathke's Pocket. Here a small ventral evagination from 

 the floor of the interbrain protrudes in the direction of the mouth 

 pouch. It has carried with it a minute lumen which opens into the 

 diencephalic cavity. This element is obviously the anläge of the 

 infundibulum and infundibular process [28]. 



10 mm Cat Embryo no. 421 (plate XIII, fig. 18). The buccal eva- 

 gination [25] has been constricted off from the mouth cavity to a 

 considerable degree, and as a result is beginning to present a definite 

 ventral surface. The dorsal surface of the pouch is still juxta-neural 



18* 



