THE STRUCTURE OF THE CEREBELLUM 



707 



The external surface of the cerebellum presents numerous deep furrows or 

 sulci which limit narrow leaf -like gyri or convolutions. Thus, when cut trans- 

 versely across, the section presents a number of lamellae, or leaf-like subdivisions, 

 which bear a close resemblance to the sprigs of the evergreen cedar tree, designated 

 as arbor vitse. Each lamella is made up of a central core of white matter and an 

 external envelope of gray matter. The latter consists of three layers. At the point 

 of contact between the cortical gray and the white matter lies a broad zone of very 

 minute granular cells. These elements possess a scanty amount of cytoplasm and 

 very short claw-like dendrites. Their axones are thin and non-medullated, and 

 connect with the constituents of the superficial molecular layer. Here they divide 

 into two branches which pursue a course parallel to the longitudinal axis of the 

 lamellae and terminate among the dendrites of the cells of Purkinje, 1 composing the 



Culmen 



Sulcus precUvalia 



Clivus 



Sulcus postcentralis 



Sulcus precentralis 



Sulcus postclivalis 

 Folium cacuininis 

 Sulcus horizontalis 

 magnus 



Sulcus precentraUt \ 



Lingul-a 



Sup. med. velum 



Dorsal recess of 



4th ventr. 



Nodulus 

 Sulcus post- 

 nodztlaris 



t 



Tuber valvula 

 Sulcus postpyramidalis 



Uvula 



JJ 



? s 



FIG. 352. MEDIAN SECTION OF THE WORM. 



Sagittal section of the cerebellum to show its internal structure, the relative depth 

 of the fissures, and the grouping of the laminae. (Schafer.) 



central layer. The cells just mentioned are the most characteristic constituents of 

 the cerebellar cortex. They present large pear-shaped bodies and a bushy fan- 

 shaped network of dendrites, which is directed transversely to the long axis of the 

 lamellae. Their axons are myelinated and form the chief efferent path between the 

 cortex of the cerebellum and the more deeply seated nuclei, to be described later. 

 The most external zone is known as the molecular. It is occupied by the dendrites 

 of the cells of Purkinje and those of the cells of the granular layer. A few neurons 

 are interposed in this place for purposes of association. The most characteristic of 

 these are the so-called basket cells. 



The fibers composing the white matter are of three kinds two afferent and one 

 efferent. The former pass either directly into the molecular layer where they 

 terminate among the dendrites of the cells of Purkinje, or extend only as far as the 



1 Named after their discoverer, Johannes Purkinje, Professor of Physiology at 

 Breslau, from 1822 to 1850. 



