ON SOME HISTOLOGICAL FEATUKES OF THE BRAIN. 653 



The Superficial Gray Matter of the Cerebellum. 



561. 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 inward to and contribute to form the central white matter of the 

 cerebellum, and of a superficial layer of gray matter. A section through 

 a lamella perpendicular to the surface shows that the gray 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 superficial pia mater a much thicker layer of peculiar nature, called the 

 molecular layer. Between these two layers, and connected, as we shall see, 

 with both of them, lies a row of very large and remarkable cells, called the 

 cells of Purkinje, the bodies of which abut on the nuclear layer, and the 

 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 lamellae, 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-branched 

 processes of the cells of Purkinje since they run in the transverse plane are 

 adequately seen in transverse sections only ; longitudinal sections show only 

 their profiles. 



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

 tion 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 nervous elements, and here perhaps even more than else- 

 where 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 processes of the cells of Purkiuje; and scattered about lie numer- 

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

 undoubtedly nerve-cells. The most conspicious feature of the layer, how- 

 ever, 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 /j. 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 nu- 

 clear 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 



