1022 HISTOLOGY OF CEREBELLUM. [BOOK m. 



corpora quadrigemina too the grey matter is broken up by sheets 

 or bundles of white matter. 



The nerve cells of the several collections of grey matter are 

 not all alike ; they present in different regions differences in size, 

 form, and in other characters. The cells of the nucleus caudatus, 

 for instance, are rather small and often round or spindleshaped, 

 while those of the optic thalamus are large, branched and rich in 

 pigment. The cells of the substantia nigra are spindleshaped, of 

 moderate size, and so loaded with black pigment (in man) as to 

 justify the name ; those of the locus caeruleus are very large and 

 spherical, with just so much pigment as to give a blueish tint. 

 But our knowledge of the finer histological details of the various 

 masses of grey matter is at present too imperfect to afford any 

 basis whatever for physiological deductions ; and it will be hardly 

 profitable to dwell upon them. Two regions of grey matter alone 

 call for special description, the cortex cerebri and the superficial 

 grey matter of the cerebellum. 



The superficial grey matter of the cerebellum. 



648. The surface of the cerebellum is increased by being 

 folded or plaited into leaf-like folds, and each of these primary folds 

 is similarly folded into a number of secondary, also leaf-like, folds or 

 lamellae. Each of these lamellae consists of a central core of white 

 matter, the fibres of which pass inwards to, and contribute to form 

 the central white matter of the cerebellum, and of a superficial layer 

 of grey matter. A section through a lamella perpendicular to the 

 surface shews that the grey matter consists essentially of two layers : 

 a layer lying next to the white matter formed by densely crowded 



/ small cells, called the nuclear layer, and between this and the super- 

 ficial pia mater a much thicker layer of peculiar nature, called the 



i- molecular layer. Between these two layers, and connected as we 

 shall see with both of them, lies a row of very large and remark- 



3 able cells, called the^cells o^Purjdn^e', the bodies of which abut on 

 the nuclear layer, anTPfche long branches of which traverse the 

 molecular layer; these cells so placed may be said to constitute 

 a third layer. Before proceeding further, we may here remark 

 that a section of the lamella, that is one of the secondary not one 

 of the primary folds, while still remaining a vertical section (that 

 is perpendicular to the surface) may be carried through the lamella 

 in different planes, and that of these several planes, the sections 

 taken in two of them are especially instructive, namely, the one 

 taken in what we may call the longitudinal plane, passing from 

 the top of the lamella to its base, and the one taken at right 

 angles to the former, in what we may call the transverse plane. 

 The nuclear layer and the molecular layer present the same broad 

 features in both longitudinal and transverse sections, but the long 



