STRUCTURE OF THE CEREBRUM. 245 



extent along their branchings, by a basket-work formed of the terminal 

 arborisation of some of the fibres of the medullary centre other than 

 those which are continuous with the axis-cylinder processes of the same 

 cells (fig. 275). The body of the cell of Purkinje is further invested 

 by a felt-work of fibrils formed by the arborisation of axis-cylinder 

 processes of nerve-cells in the outer layer of the grey matter (fig. 274). 

 Each cell has therefore a double investment of this nature, one covering 

 the dendrites, the other the body of the cell. 



The granules of the inner layer of grey matter are mostly small 

 nerve-cells, with a few extended dendrites penetrating amongst the 

 other granules, and an axis-cylinder process which is directed between 

 the cells of Purkinje into the outer layer. After penetrating a greater 

 or less distance into this layer it bifurcates, and its two branches pass 

 in opposite directions at right angles to the main stem, and parallel 

 to the direction of the lamella (fig. 273, I.). What ultimately becomes 

 of them is not known. In sections cut across the lamellae the cut ends 

 of these fibres give a finely punctated appearance to the outer layer 

 (fig. 273, II.). 



Ramifying amongst the cells of the granule-layer are peculiar fibres 

 derived from the white centre, and characterised by having tufts of fine 

 short branches at intervals like tufts of moss (fig. 275, m). These are 

 termed by Cajal the moss-fibres ; they end partly in the granule layer, 

 partly in the molecular layer. 



Structure of the cerebrum. The grey matter of the cerebral cortex 

 is described as being composed of a number of layers, but they are not 

 sharply marked off from one another, and they vary in relative develop- 

 ment in different regions of the cortex. The following are usually 

 distinguished. 



1. A thin peripheral stratum (molecular layer) containing a few 

 scattered cells, which are mostly neuroglia-cells. They tend to take a 

 direction vertical to the surface (fig. 276). In the most superficial 

 part of this layer, immediately under the pia mater, is a thin stratum 

 of medullated nerve-fibres, and besides these the layer contains a large 

 number of non-medullated fibres, many of which are ramified. They 

 .are derived from the nerve-processes of some of the deeper nerve-cells 

 of the cortex. Intermingled with these fibres are a certain number of 

 ramified nerve-cells, most of which have two (sometimes three) axis- 

 cylinder processes, all of which terminate by arborisation within the 

 superficial layer. 



2. A layer of closely set small pyramidal nerve-cells several deep 

 (layer of small pyramid*). 



3. A layer of medium-sized pyramidal cells less closely set, with 



