THE PON'S AND THE OEEEBELLUM. 339 



granulosa it is completely lacking in healthy persons. In paralytics, however, Wei- 

 gert, on whose authority these statements are made, found a very marked exuber- 

 ance of the glia. From the region of the cells of Purkinje to the innermost layer of 

 the zona molecularis lie small slender plexuses, while within the molecular lay,er 

 itself there are found relatively sparingly thick fibers, which extend perpendicularly 

 to the surface: the Bergmann-Deiter fibers. The surface of the normal cerebellum 

 lacks the superficial glia-net usually present on the surface of the central nervous 

 system. But in all embryos — even in non-mammals — one finds, as outermost layer 

 of the cerebellum, one or more strata of spheroidal cells which are later lost. 



The outer surface of the cerebellum was described by Malacarne, Eeil, 

 and Burdach as we know it to-day. The investigation of its inner structure 

 was accomplished by F. Arnold, Eeil, Kolliker, Meynert, and especially by 

 B. Stilling. More recent investigations on the constitution of the peduncles 

 were made by Bechterew, Marchi, Minghazzini, Perrier and Turner, and 

 by Pellizzi. On the cortex of the cerebellum there is a voluminous litera- 

 ture to which especially Purkinje, Gerlach, Kolliker, F. E. Schultze, Ober- 

 steiner, and Bevor furnished contributions. But only through the studies of 

 Golgi, Eamon y Cajal, Kolliker, and Gehuchten does one obtain an exact 

 understanding of the structure. Here, as in so many other places, the im- 

 provement of the technique made possible an advance where the most dili- 

 gent simple observations would have revealed little. 



Diseases of the cerebellar peduncles alone are very seldom observed. 

 Thus, little is known of the symptoms which are to be expected in the case of 

 such a disease. Gradual destruction of one brachium pontis may apparently 

 give rise to no symptoms. In diseases which produce an irritation — for 

 •example, hemorrhages and tumors — forced movements frequently occur, 

 such as rolling from side to side. A forced position of the trunk or of the 

 head alone, with or without nystagmus, has been observed in irritating 

 diseases of one of the arms of the pons. 



For the determination of the symptoms conditioned upon diseases of 

 the cerebellum we are guided primarily by the quite frequent tumors, and 

 secondarily by the not infrequent abscesses which accompany purulent 

 inflammations of the ear. Hemorrhage, softening, arteriosclerosis, and 

 ■other pathological processes occur in the cerebellum; but these diseases are 

 €ither very infrequent and usually not confined to the cerebellum, or they 

 lead — as is the case of hemorrhages — so quickly to death that no time 

 is offered for the development of a special combination of cerebellar symp- 

 toms. In the case of tumors, and, in a somewhat less degree, in abscesses 

 of the brain, there exists simply the difficulty that we are not justified in 

 attributing all of the symptoms which appear directly to the lesion of that 

 part of the brain involved in the tumor. Besides the so-called local phe- 

 nomena, the tumor nearly always induces two other groups of symptoms: 



