436 J. TtKaham keur. 



dilated at its distal end, and lying between the choroid 

 plexuses. The paraphysis does not give rise to plexus 

 itself, nlthoug'h, from its very close relations with the choroid 

 plexus on each side, it may on superficial examination appear 

 to do so.^ 



On the floor of the thalamencephalon it has already been 

 seen that the preoptic recess becomes distinct very early, 

 marking off the region of the chiasma from that of the 

 anterior commissure. The tip of the infundibulum remains 

 quite simple as far as Stage 38, but in Stage 39 it is found 

 to have sprouted out into narrow, tubular, and apparently 

 glandular diverticula, which, winding hither and thither, 

 fuse with and to a certain extent penetrate the dorsal part of 

 the hypophysis, forming the so-called nervous part of the 

 hypophysis. 



I must again draw attention to the curious differential 

 growth in the anterior part of the floor of the thalamen- 

 cephalon, which leads to a migration forwards and upwards 

 of the anterior commissure, so that this structure, which at 

 first lay on the floor of the thalamencephalon, comes to be 

 situated well up on its anterior wall. The anterior com- 

 missure by the early appearance of its rudiment performs 

 an important service, for it acts as a landmark to indicate 

 the position of the anterior end of the longitudinal axis of 

 the base of the original brain rudiment, which lies just in 

 front of it. From this follows the important consequence 

 that the front termination of this original axis lies in the 

 adult Lepi do siren, by no means at the tip of the infun- 

 dibulum, but high up on the anterior wall of the thalamen- 

 cephalon. 



It will have excited attention that I have, in treating 

 of sagittal sections, said nothing about the velum. The 

 velum is in fact a paii-od structure. In accurately mesial 

 sections the anterior wall of the thnlnniencephalon is as 

 shown in the figures, but upon either side of the mesial plane 



' In tliis I entirely agree witli Minot, op. cit., p. 95. 



