518 



Prof. A. Dendy and Mr. G. E. Nicholls. 



[May 24, 



epithelium of the sub-commissural organ (s.c.o.), which is continued round 

 the anterior end of the posterior commissure for a short distance on to the 

 floor of the infra-pineal recess, where it gradually loses its columnar 

 character. Beneath the epithelium are seen portions of Eeissner's fibre (?•/.), 

 whose branches, no doubt, are connected with the epithelial cells as in lower 

 types, and as in the cat to be described later on. 



It will be noticed that the epithelium of the sub-commissural organ is 

 thrown into a transverse fold near its anterior end, just before it turns 

 round over the anterior end of the posterior commissure. Towards its hinder 

 extremity it appears to become discontinuous, and two little separate islands 



Fio. 2.— Mouse. Transverse Section through the Region of the Posterior Commissure, 

 taken at about the level of the line fih in fig. 1. x lOrj. 



c.p., choroid plexus ; i.p. r., infra-pineal recess ; p. c, posterior commissure ; 

 t.c. o., sub-coiamisaural organ ; s.p. r., supra-pineal recess ; v., veins. 



