720 BR JAMES W. DAWSON ON 



towards the ventricle from the surface of the medulla : this cuts across the fibres passing 

 from the inferior olive to the restiform body and involves the nucleus ambiguus and the 

 adjacent portion of the forniatio reticularis. From the angle of the ventricle on the opposite 

 side a dense band also passes to the surface of the medulla : this involves the fibres of the 

 Vlllth nerve, the acoustic tubercle, the outer portion of the restiform body, and a portion 

 of the peduncle of the flocculus. Narrow zones of sclerosis are also present on this side 

 between the pyramid and the mesial fillet, and between the pyramid and the inferior olive. 

 A few minute areas occur in the hilum of each inferior olive and amongst the fibres of the 

 mesial fillet. The lateral walls and roof of the ventricle are more involved than the floor, 

 and large areas of an " early " type pass from the ventricular surface into the hilum of each 

 dentate nucleus. Further areas are found in different stages of development in the cere- 

 bellar white matter, especially at its junction with the folia : the cores of the folia of both 

 nocculi and of the vermis are markedly involved. 



Pons Varolii. — Lower Third. — The angles of the ventricle and lateral walls are again 

 more affected than the floor, and the sclerosis is continuous along the lateral walls to the 

 hilum of each dentate nucleus : on one side the whole ventral half of the dentate nucleus 

 is denwelinated. Several areas, mostly of early type, occur in the central white matter of 

 the cerebellum and at its junction with the folia. Denser areas are present amongst the 

 pyramidal fibres and early areas in the formatio reticularis on both sides. 



Middle Third. — The most affected parts lie in relation to the angles of the IVth ven- 

 tricle. From one a large area spreads outwards and forwards : it completely obliterates 

 Deiters' and Bechterew's nuclei and the restiform body fibres, and extends for a consider- 

 able distance into the cerebellar white matter. From the opposite angle the sclerosis extends 

 along the floor of the ventricle as far as the median raphe : it obliterates the Vlth nerve 

 nucleus and the genu of the Vllth nerve, extends for a short distance into the formatio reticu- 

 laris, and from the angle a diffuse area extends into the cerebellar white matter and along 

 the lateral wall to the roof of the ventricle. 



Upper Third (fig. 222).- — The same two areas, in relation to the angles of the ventricle, 

 appear at this level : one of these passes into the middle peduncle, involving the motor and 

 sensory Vth nuclei and several of the adjacent cerebellar folia? : the opposite area is much 

 smaller, but a diffuse zone extends around it to occupy a position similar to the affected 

 tissue on the opposite side. Smaller patches occur among the transverse fibres of the pons, 

 and larger areas towards the ventral aspect of the pyramidal bundles. At a higher level 

 (fig. 223) both the areas in relation to the ventricle have disappeared — the peri-aqueductal 

 tissue being normal. An irregularly wedge-shaped area is present on the ventral surface 

 of the pons to one side of the middle line, a similar area passes inwards from the surface 

 at a point just ventral to the superior cerebellar peduncle, and several early areas lie in the 

 middle peduncle and in the formatio reticularis on both sides. 



At the level of the inferior quadrigemina (fig. 224) a slight peri-aqueductal sclerosis 

 occurs : this does not involve the posterior longitudinal fasciculus, but extends into the 

 quadrigeminal bodies for a short distance. A small area is present in the middle line in 

 front of the decussation of the superior cerebellar peduncles — an area which higher up 

 extends to involve part of the mesial fillet and surrounding fibres. A larger area passes 

 inwards for a short distance amongst the anterior superficial pontine fibres on one side, 

 and at a slightly higher level several small areas are found in relation to the anterior and 

 lateral surfaces. 



Horizontal sections through the optic chiasma (fig. 225) show that the myelin stains 

 faintly over the whole optic chiasma, both optic nerves, one optic tract, and part of the 

 other. There is a narrow zone of complete demyelination in the anterior margin of the 

 chiasma, which extends forward along the inner border of one optic nerve : the septal con- 

 nective tissue and vessels of both optic nerves are very thickened. 



