THE BRAIN 511 



matter of the spinal cord, that is to say, it is made up 

 chiefly of niedullated nerve fibres. Portions of this white 

 matter extend outwards into the primary foldings and 

 secondary lamellae of the cerebellar surface, and are 

 covered by grey matter, the arrangement thus presenting 

 a very characteristic arborescent appearance when seen in 

 section.' 



When a section of the external grey matter is cut at 

 right angles to the surface of a lamella, stained, and ex- 

 amined under the ijiicroscope, it is found to consist of two 

 layers. The innermost, lying next to the central white 

 matter, is made up of a large number of small closely- 

 packed cells supported by neuroglia (see p. 465) and is 

 known as the nuclear layer (Fig. 164, N). The outer 

 layer, immediately under the pia mater, shows a few cells, 

 but the chief appearance it presents is that of a granular 

 mass made up of closely-set dots. These dots are in 

 reality the cut ends of fibres of which some belong to 

 the supporting neuroglia, but of which the majority are 

 nerve fibrils. From its punctated appearance (Fig. 

 164, X.) this layer, which is much broader than the 

 nuclear layer, is known as the molecular layer 

 (Fig. 164, M.). Between these two layers lies a row of 

 nerve cells of very striking and characteristic appearance, 

 known as the cells of Purkinj^ (Fig. 164, 1). These 

 are pear-shaped, with a large and conspicuous nucleus, 

 the bulbous inner end resting on the nuclear layer, 

 while the outer end divides into a large number of 

 processes which run out into the molecular layer as finer 

 and finer branches. The granular apjjearance of the 

 molecular layer is in part due to the close j uxtaposition of 

 the cut ends of these branches or dendrites from the cells of 

 Purkinje. The inner end of each cell bears a single process 

 which is usually cut through near the cell but is really pro- 

 longed down into the central white matter as a niedullated 

 nerve fibre. Such are the details which can be made out 

 1 This is somewhat imperfectly shown in Figs. 161 and 163. 



