THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 631 



At a slightly higher level (fig. 45) the mesial patch is found to extend inwards 

 only a short distance from the surface, while another patch, commencing close to it, 

 passes round the periphery of the pons on one side. Numerous other patches are 

 present on the transverse section : three small areas towards the middle line ; one, 

 which reaches forwards from the aqueduct of Sylvius and extends laterally to involve 

 the posterior part of one superior cerebellar peduncle ; and another small area at the 

 anterior level of this peduncle. 



Still higher (fig. 46) sclerosed areas are present on the surface of the pons — on 

 one side extending inwards to involve the mesial fillet. The sclerosis round the 

 aqueduct of Sylvius involves it completely and sends a small projection forwards. 

 In the centre of one pyramid a round " shadow " patch can be clearly identified, a 

 second similar area is present in the middle line at the level of the mesial fillet, and 

 a third at the lateral border of the mesial fillet. 



Mid-Brain (fig. 47). 



The aqueduct of Sylvius is now free, but an area occupies the mesial line in front 

 of the commencing decussation of the superior cerebellar peduncles and another is 

 found laterally and slightly posterior. A triangular area of sclerosis in the middle 

 line extends inwards from the anterior surface, and two smaller lateral areas are 

 present, one on the surface and one slightly internal. These areas are all sharply 

 marked off from the surrounding tissue and bear no relation to any of the structures 

 through which they pass. 



Sub -thalamic Region. 



In sections at this level an irregular patch is found in the anterior half of the 

 mesial plane. The sclerosis extends outwards on each side into the red nucleus, and 

 there are several small but well-defined areas in the ansa lenticularis on both sides. 

 The aqueduct of Sylvius is surrounded by an oval patch, which extends outwards 

 slightly beyond the grey matter. 



Cerebral Hemispheres. 



(l) Horizontal sections through the cerebral hemispheres at the lower part of the 

 basal ganglia (figs. 23, 24). 



Peri-ventricular sclerosis. — The most prominent lesion is that found at the 

 posterior cornua of the lateral ventricles. These are both surrounded by large 

 irregular areas of sclerosis, which extend at several points through the white matter 

 to reach the surface of the brain. This is well marked on the inner side of both 

 posterior horns, where the sclerosis cuts across the tapetum, the inferior longitudinal 

 bundle, and the splenium, and reaches the surface at the parieto-occipital fissure. 

 On the right side this area is continuous with another which extends from the 



