488 Prof. A. Dendy. On a Pair of Ciliated Grooves 



the epithelium which lines the grooves to that which lines the adjacent 

 parts of the brain-cavity takes place abruptly, and there are indications 

 on the latter of very much longer cilia than occur in the grooves. 

 As far back as 1873, indeed, Langerhans pointed out in his researches 

 on Petromyzon platwi that the ventricles of the brain are lined with 

 ciliated cylinder-epithelium.* 



The upper and inner part of each groove is in this region imbedded 

 in the substance of the posterior commissure ; the lower and outer 

 portion in the mass of cells which forms the inner part of the brain 

 substance (fig. 2). Anteriorly the two grooves diverge from one 

 another on the roof of the recessus sub-pinealis, and disappear in 

 the deep crevices between the ganglia habenulse and the side walls 

 of the brain. Posteriorly they terminate at the hinder margin of the 

 posterior commissure. Immediately behind this point the choroid 

 plexus of the mid-brain dips down into the aquseductus Sylvii, or iter, 

 in the shape of a thin vertical lamella, which forms a highly vascular 

 longitudinal septum dividing the upper part of the iter into right 

 and left halves (fig. 3). The anterior portion of this septum is visible 



N.C 



Tr. 



in sections beneath the ciliated grooves in the region of the posterior 

 commissure (fig. 1), while it extends backwards throughout the 'whole 

 or very nearly the whole length of the mid-brain. 



Thanks to the kindness of Dr. S. J. Hickson, F.R.S., Professor of 



* ' Berichte iiber die Verlmndlungen der NaturforscLenden Gcsellschaft zu 

 Freiburg i. B.,' vol. 6, Heft 3, p. 83. 



