DEGENERATIONS FOLLOWING CEEEBELLAR LESIONS. 93 



of the cerebellar lamellae (fig. 70, A, B). But the further development of these cells has not as 

 yet been ascertained, and it can only be conjectured that they become gradually transformed into 

 cells of the molecular layer, for no such superficial zone can be seen in the adult cerebellum. 

 At early stages of development there are also to be seen in the molecular layer, bipolar cells 

 placed with their axes vertical, and having protoplasmic processes extending down towards or 

 into the rust-coloured layer, and axis-cylinder processes extending towards the surface, and 

 becoming continued by T-shaped junctions into fibres running parallel with the processes of 

 the horizontal bipolar cells which have just been described. These vertical bipolar cells may 

 perhaps be derived from the horizontal ones, and represent a stage in the formation of the 

 smaller granules of the rust-coloured layer, but we have no clear evidence as to their further 

 course of development. Like the superficial granules they also are only found in young 

 animals. The cells of Purkinje in the cerebellum of embryonic and very young animals are 

 very irregular multipolar cells, with relatively short protoplasmic processes, but a well- 

 developed axis-cylinder process, which already has two or three collateral fibres extending 

 towards and ramifying in the deeper part of the molecular layer (fig. 69). It is not until two or 

 three weeks after birth (in the dog) that the dendrites begin to assume the characteristic form 

 and arrangement. The arborescence which in the adult cerebellum envelopes the principal 

 dendrites of the cells of Purkinje (see p. 91 and fig. 67), is at this early stage chiefly con- 

 fined to the upper part of the body of the cell (fig. 70). 



DEGENERATIONS FOLLOWING CEEEBELLAR LESIONS. 



The degenerations of nerve-fibres which follow lesions of the cerebellum have 

 been investigated by Marchi in animals (dogs and monkeys) operated upon by Luciani. 



Hemiextirpation (see fig. 71). After removal of one half of the organ 

 extensive degeneration is seen in all three peduncles of the same side ; very little, if 

 any, in the peduncles of the opposite side. It may therefore be inferred that none 

 of the peduncles contain commissural fibres connecting the two halves of the organ. 



The degenerated fibres in the superior peduncle pass partly to the tegmental nucleus 

 of the opposite side, and partly to that of the same side ; in other words, the decus- 

 sation of these peduncles in the region of the inferior corpora quadrigemina is not 

 complete. Some fibres can be traced as far as the optic thalamus. 



The middle peduncle, after removal of the corresponding half of the cerebellum, 

 is completely degenerated as far as the raphe. Degenerated fibres are seen inter- 

 mingled with the pyramidal fibres both of the same side and of the opposite side, 

 and with the fibres of the fillet and posterior longitudinal bundle, mainly of the 

 same side. Degeneration and atrophy are also produced in the grey matter of the 

 pons (nuclei pontis) of the same side. The degeneration in the fillet and posterior 

 longitudinal bundle is most marked on the side of the lesion ; it can be followed 

 upwards to the region of the corpora quadrigemina, and downwards to a tract at the 

 periphery of the antero-lateral column of the spinal cord. A bundle of degenerated 

 fibres is also seen passing to the pyramidal tract. These appear to pass upwards 

 towards the corpora quadrigemina, and probably to the corpus striatum, chiefly 

 of the same side ; a few are traceable downwards into the cord. 



The inferior peduncle, after hemiextirpation of the cerebellum, is notably 

 degenerated in its inner and outer parts. A small degenerated bundle is traceable 

 with the inner arched fibres, across the raphe to the opposite lower olive which 

 undergoes complete atrophy ; other arched bundles pass from the restiform body to 

 the tract of the fillet, and of the posterior longitudinal bundle of the same side ; 

 and from these, as above stated, many degenerated fibres are traceable down the 

 periphery of the antero-lateral column of the cord, some down the pyramidal tract, 

 but most are situated ventral to the direct cerebellar tract of Flechsig in the 

 antero-lateral descending cerebellar tract. 



It is also stated by Marchi that after hemiextirpation of the cerebellum, degene- 

 rated fibres are seen passing along with the roots of nearly all the cranial nerves, 

 especially the second, third, fifth (ascending root), sixth, seventh, and twelfth, and 



