THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 629 



irregularly-shaped patches. On the one side the outer half of the pyramid and of the 

 inferior olive, together with the whole of the restiform body and the intermediate 

 structures, are affected. On the opposite side the posterior outer quadrant of the 

 inferior olive is involved in an area which sends a small prolongation into the 

 formatio reticularis, and extends upwards to involve the outer parts of the restiform 

 body — leaving the fibres in the middle intact and connected with the formatio 

 reticularis by a narrow band of normal fibres. The entering VHIth nerve on each 

 side passes directly into sclerosed tissue ; the fibres in their extra-medullary course 

 stain normally. The vermis and the accompanying nodules are also involved, and 

 the sclerosed area extends on each side of the roof of the IVth ventricle, and passes 

 into the hilum of the dentate nucleus — involving on one side the grey matter of the 

 nucleus. Several of the medullary cores of the folia of the flocculus are demyelinated 

 (figs. 27, 28, 39). 



Pons Varolii. 



As we ascend the brain stem the sclerosis becomes still more marked ; the 

 structures lining the floor of the IVth ventricle are particularly affected, and in the 

 lower part of the pons both lateral angles are profoundly altered (fig. 39). 



At the level of the lower third of the middle peduncles (fig. 40) patches are found 

 reaching from the ventricle to the surface. The sclerosed area involves nearly the 

 whole of one side of the pons, and extends over the median raphe to affect all the 

 fibres of the mesial fillet : on this side the middle two-thirds of the pyramid escape 

 together with a small tongue-like projection of normal fibres passing upwards into 

 the inferior olive. The sclerosis here extends backwards along the floor of the 

 ventricle and the lateral angle to the roof, and also laterally to involve the centre of 

 the corresponding flocculus. On the opposite side a small area is present external to 

 the inferior olive. The sclerosed tissue cutting across the middle peduncle is con- 

 stricted in the middle, and thus is divided into two areas — one at the corner of the 

 ventricle, and the other, at the zone of entry of the VHIth nerve, extends into the 

 white matter of the cerebellum and the corresponding flocculus. In the cerebellar 

 white matter two small isolated patches are found, while in the folia several separate 

 areas are present — one of which involves the vermis, two the junctions of the white 

 matter and the folia, and others cut across the medullary cores of individual folise. 

 The cranial nuclei in this region, which was cut serially, are all involved, the nuclei 

 of the Vlth nerve, the cochlear nuclei, and the nuclei of Bechterew and Deiters. 



Slightly higher (fig. 41) the only normal tissue is in the middle line, both middle 

 peduncles being obliterated. The normal tissue is intersected by several small areas 

 in different stages of sclerosis, and is separated from the IVth ventricle by a broad 

 band. On the one side the sclerosis of the middle peduncle involves the whole of 

 the restiform body, the emerging root-entry zone of the Vlllth nerve and the 

 associated nuclei, and extends round the angle of the ventricle to the roof. Laterally 



TRANS. ROY. SOC. EDIN., VOL. L, PART III (NO. 18). 88 



