280 Frederick Tilney, 



brain. Although the tuberai processes [30] are still independent of 

 each other, they have grown in toward the median line and' are thus 

 drawing closer together in this direction. In addition to a marked 

 increase in the size of the caudal horn of the tuberai sprout there 

 has now appeared a cephalic horn on each process. This horn is 

 relatively short and extends cephalad far enough to apply itself to 

 the cephalic extremity of the saccular eminence. The two cephalic 

 horns are separated by only a short distance across to the median line. 



The original caudal projections from the body of the sac are no 

 longer apparent since they have now fused across the mid-line and 

 provided the ventral surface of the infundibular process with a com- 

 plete epithelial covering. In this manner the infundibular process is 

 entirely invested by epithelium as a result of the extension of the 

 primitive juxta-neural relation established between this process and 

 the buccal sac. Only a small portion of the median ridge of the 

 dorsal surface of the sac has retained its juxta-neural position and 

 even this is yielding in places to the advance of the tuberai sprouts 

 as they are approaching each other across the median line to form 

 a complete epithelial investment about the eminentia saccularis. The 

 infundibular process, which in the earlier stages has increased in 

 length from its cephalic extremity, now reverses this direction and 

 presents a marked increment to its caudal extremity. The saccular 

 eminence, without any gain in surface prominence, is still well defined, 

 while the recessus tuberis has not only increased in its transverse 

 diameters, but this transverse expansion now extends from the post- 

 chiasmatic process as far caudad as the infundibuhnn. 



51 mm Cat Embryo no. 104 (plate XIV, fig. 22). 



One change of moment characterizes this stage; i. e. the cephalic 

 horns of the tuberai processes have met across the median line and 

 fused. The ventral surface of the saccular eminence is thus entirely 

 covered by epithelium. The fusion between the tuberai sprouts is 

 not limited to these cephalic horns and as a result only a very small 

 portion of the dorsal surface of the original sac is now juxta-neural 

 in position. By the appearance of two lateral protuberances, one on 

 either side of the saccular eminence, the tuber cinereum has acquired 



