278 Frederick Tilney, 



sprout lias grown dorsad and assumed a juxta-neural position along- 

 a small area of the floor of the diencephalon. It is evident that this 

 growth of the tuberai process is in part responsible for forcing the 

 dorsal surface of the pars buccalis out of its juxta-neural position. 

 In the region where the tuberai sprout has attained its greatest 

 height, the dorsal surface is separated by the greatest distance from 

 the brain tissue. The tuberai process has not only increased in alti- 

 tude and become juxta-neural in position but it has thrown out a 

 cornu which is extending backward in the direction of the caudal 

 projections. The latter projections still adhere to the infundibular 

 process along its dorsal aspects, while the caudal extremity of the 

 buccal sac is in contact with the cephalic extremity of the processus 

 infundibuli. The ventral surface of the latter process is as yet un- 

 covered by epithelium. 



The pars neuralis presents no marked change from the earlier 

 stages. The infundibular process appears to have ceased its ventral 

 growth; it retains its original cavity which communicates with the 

 third ventricle by means of a small canal. This cavity will later 

 assume the dimensions of the recessus processi infundibuli while the 

 canal becomes the processus infundibuli. In the floor of the ventricle 

 there are two well marked levels, the more cephalic and higher 

 corresponding to the post chiasmatic process, while the lower level 

 forms the floor of the recessus tuberis. 



25 mm Cat Embryo No. 147 (plate XIV, fig. 20). 

 The changes in the pars buccalis which distinguish this stage 

 are the rapid growth in the tuberai process, its general disposition 

 to become more juxta-neural in its relations, and the attendant dis- 

 placement of the dorsal surface of the buccal sac from its original 

 close contact with the brain tissue. The right and left tuberai pro- 

 cesses are still independent of each other; each is attached to the 

 pars buccalis at the junction of the body and neck of that structure; 

 each presents a long caudal and a short cephalic horn. The tuberai 

 process [30] is now in contact with the brain and thus forms a large 

 juxta-neural element. The configuration of the sac has changed con- 

 siderably, due to the fact that the caudal projections [25a] are ap- 



