716 [Recess, 



II. " Notes of Researches on the Intimate Structure of the 

 Brain." Third Series. By J. LOCKHART CLARKE, F.R.S. 

 Received September 1, 1863. 



Structure of the Valve of Vieussens. The valve of Vieussens 

 consists of four different kinds of layers. The most inferior layer is 

 composed of epithelium, which is continuous with that of the fourth 

 ventricle. The second layer is a stratum of longitudinal nerve-fibres, 

 continuous with the white substance of the inferior vermiform pro- 

 cess of the cerebellum. The third layer consists of a multitude of 

 round, granular nuclei of about the 3500th of an inch in diameter, 

 traversed by fibres derived from the subjacent layer. These nerve- 

 fibres, in my preparations, may be seen in the most unequivocal 

 manner to divide and subdivide into small branches, to which the 

 nuclei are attached as by stalks. The/bwr^A or uppermost layer is 

 chiefly granular, but is also interspersed with nuclei of the same 

 kind. Along its under side, where it joins the preceding layer, is a 

 row of large multipolar cells, which are connected by their processes 

 with the nuclei of both layers*. 



Structure of the Cerebral Convolutions. In the human brain 

 most of the convolutions, when properly examined, may be seen to 

 consist of no less than eight distinct and concentric layers. This 

 laminated structure is most marked at the end of the posterior lobe. 

 On cutting off the rounded point of this lobe in the human brain, 

 by a transverse section, at about the distance of an inch, measured 

 along the side of the longitudinal fissure, I found, at this part, that 

 the stratified appearance was very indistinct in the upper and outer 

 convolutions, while it was still clearly observable in the inner and 

 lower convolutions which rest on the cerebellum. It was most con- 

 spicuous in the convolution that lies over the bottom of the posterior 

 notch of the cerebellum, and which runs outward and upward, and 

 then winds inward, to reach the surface at the side of the longi- 

 tudinal fissure. 



In vertical sections of convolutions taken from the end of the 

 posterior lobe, where the laminated structure is most marked, the , 



* This description of the valve of Vieussens formed part of the manuscript 

 of a Paper published in the ' Proceedings of the Royal Society ' for June 20, 1861, 

 but \vas accidentally omitted in the printing. 



