THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 709 



The posterior columns are occupied by an advanced patch : the anterior and antero-lateral 

 by early sclerosis, but towards the lateral margins of the cord on both sides areas of more 

 dense sclerosis are present in the centre of early diffuse areas. The only fibres unaffected 

 are those at the tip of the posterior horns and at the lateral and anterior periphery of the cord. 



Dorsal Region (figs. 170-173). — In the upper dorsal segments, the posterior columns 

 are densely sclerosed. There is evidence of early involvement of the. crossed pyramidal 

 tract on both sides. The grey matter is almost unaffected ; and a few normal fibres are 

 found at the periphery of the posterior columns. At the level of the third and fourth segments 

 the areas have increased in size, and the normal fibres form a narrow zone round the antero- 

 lateral margin. About the middle dorsal region the single area found above is again broken 

 up, and three areas are present. One occupies the middle two-thirds of the posterior columns, 

 and the other two are in the centre of the lateral columns. These patches are continued, 

 without any very great change, throughout the whole middle dorsal region, the two lateral 

 areas then diminish in size, while the posterior one increases, and in the lower dorsal segments 

 occupies the greater portion of the posterior columns. 



Lumbro-sacral Region (figs. 174-176). — The upper lumbar segments show little involvement, 

 but in the fourth segment five separate areas occur : one at the tip of the posterior horns 

 on each side, one has picked out the postero -lateral group of cells in the anterior horn of the 

 left side, another occupies a similar area on the opposite side, but has extended to involve 

 the white matter lying between it and the surface of the cord, and the remaining area forms 

 a circular ring around the central canal. The marginal glia zone varies considerably in 

 thickness, and at the lateral margins shows extensive development. In the fifth lumbar 

 segment diffuse early sclerosis is found towards the middle line in the posterior and antero- 

 lateral columns. In the sacral cord the sections are normal, with the exception of a possible 

 narrow ring of sclerosis around the central canal and an increase in width of the lateral 

 marginal glia. 



Medulla. — Just above the decussation of the pyramids (fig. 158), one large area is present 

 on the antero-lateral portion of one-half of the medulla, extending inwards to involve the 

 lateral nucleus, the emerging spinal accessory nerve, and the corresponding decussating 

 pyramidal fibres. A smaller but earlier area is present in the same position on the opposite 

 side, and a third, quadrilateral, area surrounds the central canal and extends on each side 

 into the nucleus gracilis. At the lower level of the inferior olive (fig. 159) these three areas 

 are still found — one of which involves the inferior olive and is continuous with the peri- 

 central area. In the region of the middle medulla (fig. 160) the internal two-thirds of the 

 left inferior olive is occupied by an area of sclerosis, which blocks up the hilum and extends 

 across the middle line to involve the mesial third of the opposite fillet, and a portion of 

 the posterior pyramidal fibres. A further area is found in the position of the substantia 

 gelatinosa Rolandi : it involves all the descending root of the Vth nerve, but is separated 

 from the periphery by normal fibres. There is also an area around the central canal and 

 a small one in the formatio reticularis, through which the fibres of the mesial fillet pass 

 previous to their decussation. 



Lower Pons (fig. 156). — The patches here are found in two positions : firstly, around the 

 floor and angles of the ventricle ; and secondly, at the lateral sides of the pons, close to the 

 Vlllth root. The former areas are extremely irregular : they do not involve the dentate 

 nucleus but send anteriorly a number of projections which involve the whole of one resti- 

 form body, the posterior portion of the other, and all the nuclei along the floor of the ventricle. 

 A well-marked oval area is present in the right mesial fillet, and early diffuse patches in both 

 pyramids. On the left side a dense area extends from the corresponding pyramid to the 

 root of the Vlllth nerve, and on the opposite side of the Vlllth nerve a large patch is present 

 extending from the angle of the ventricle to the surface of the middle peduncle, but inter- 

 sected by two strands of normal fibres. Other areas are present in the middle of the formatio 



TRANS. ROY. SOC. EDIN., VOL. L, PART III (NO. 18). 98 



