CHAP, ii.] THE BRAIN. 1023 



branched processes of the cells of Purkinje' since they run in the 

 transverse plane are adequately seen in transverse sections only, 

 longitudinal sections shew only their profiles. 



The molecular layer is of a peculiar nature. In many modes 

 of preparation and in many sections it appears chiefly composed of 

 a granular or dotted ground substance ; hence the name molecular, 

 as if it were an aggregation of molecules. The dots however are 

 sections of fine fibrils, some of which are neuroglia fibrils but others 

 are undoubtedly nervous. The layer consists in fact partly of 

 a bed of neuroglia and partly of nervous elements, and here 

 perhaps even more than elsewhere it is extremely difficult to say 

 with regard to many of the elements whether they are neuroglial 

 or nervous in nature. A considerable portion of the whole area of 

 the molecular layer is taken up by the conspicuous branched pro- 

 cesses of the cells of Purkinje ; and scattered about lie numerous 

 small cells, some of which are neuroglia cells, but some of which 

 .are undoubtedly nerve cells. The most conspicuous feature of the 

 layer however is the presence in large numbers of the fine fibrils ; 

 but before we speak of these it will be desirable to turn to the 

 cells of Purkinje and the nuclear layer. 



The cell of Purkinje possesses a large (40 p by 30 //,) flask-shaped 

 body, 'surrounding a large conspicuous clear, rounded, nucleus; it 

 has much the appearance of a large ganglion cell. The base of the 

 flask rests on the nuclear layer, and from it there proceeds a single 

 axis cylinder process which passing through the nuclear layer 

 somewhat obliquely, and in its passage acquiring a medulla, joins 

 the central white substance as a medullated fibre. The cells as 

 we have said form a single layer only, but since this covers the 

 nuclear layer over the whole of the lamella, a considerable number 

 of the fibres of the white central matter, though only a very small 

 fraction of the whole, are thus derived from these cells of Purkinje. 

 The narrowed neck of the flask running outward in the molecular 

 layer divides in an arborescent fashion into a large number of 

 branches which, spreading out laterally in the transverse plane 

 and stretching as far as the surface, ramify through the molecular 

 layer, and are eventually lost to view as exceedingly fine fibrils. 

 Some observers maintain that some of the fine processes are 

 continuous with processes of the small nerve cells of the molecular 

 layer, but this is not admitted by all. In any case the fibrillar 

 terminations of these cells of Purkinje' contribute to the fine fibrils 

 of the molecular layer. 



The nuclear layer in ordinary stained specimens has the 

 appearance of a mass of nuclei closely crowded together in a bed 

 of reticular nature ; and since the nuclei usually stain deeply, 

 the layer stands out in strong contrast to the much less deeply 

 stained molecular layer. Careful examination with special modes 

 of preparation shews however that while some of the nuclei are 

 nuclei belonging to neuroglia and blood vessels, the majority 



F. 65 



