710 DR JAMES W. DAWSON ON 



reticularis, at the posterior part of the olivary nucleus, and around the entrance of the right 

 Vlllth nerve. 



At a slightly higher level the areas are still more numerous and more extensive. Those 

 along the floor of the IVth ventricle now extend to the anterior end of the dentate nucleus. 

 Deiters' and Bechterew's nuclei and the posterior longitudinal fasciculus on both sides 

 are all involved. Both mesial fillets show large oval patches, and the whole of one pyramid 

 with the adjacent grey matter and transverse fibres of the pons are sclerosed. A dense 

 area, including three-quarters of the opposite pyramid, extends to the entry zone of the 

 Vlllth nerve, and from both angles of the ventricle a broad area extends to the surface 

 of the pons, practically isolating it from the cerebellum. 



Pons at Level of the Vth Nerve Root (fig. 157). — Here the areas are again best developed 

 at the angles of the ventricles. From this they spread along the floor of the ventricle to 

 meet in the middle line and from the right angle upwards to the roof of the ventricle, and 

 both inferior peduncles are involved as they pass to the dentate nuclei. A large early patch 

 is 'present in the left pyramid and adjoining grey matter and transverse fibres, and on 

 the opposite side the outer half of the pyramid is affected. The intra -medullary portion 

 of the left Vth nerve, immediately in its entrance, is markedly affected, and a smaller area 

 involves the opposite nerve fibres. A number of smaller areas are found in the formatio 

 reticularis and just anterior to it. 



Upper Pons. — Extensive sclerosis is present around the aqueduct. This reaches into 

 the superior cerebellar peduncle on both sides, and on the left passes through the peduncle 

 to the surface. These areas also extend anteriorly through the formatio reticularis to involve, 

 on one side, the whole of the mesial fillet and adjoining pontine fibres. Amongst the latter 

 a number of smaller patches are irregularly distributed. On the opposite side a single 

 large area occupies the outer two-thirds of the pyramid and adjoining grey matter, reaching 

 to the surface of the pons. The Vlth and Vllth nuclei on both sides are affected, as well 

 as both motor roots of the Vth nerve. 



Mid-Brain (fig. 161). — A triangular area is found around the aqueduct : this extends 

 to involve the third nucleus on both sides. Both red nuclei show irregular areas on their 

 dorsal aspect : that on the right extends through the substantia nigra into the crus, where 

 a circular patch extends about half-way to the surface in its middle third. Another large 

 irregular area is found on the opposite side at the point of emergence of the Illrd nerve : 

 this area passes upwards into the ventricle part of the corresponding red nucleus. At a 

 slightly higher level the red nucleus is not so extensively involved, but the patches in the 

 crus become more extensive. 



Cerebral Hemispheres. — At Level of Lower Border of Optic Thalamus. — The area around the 

 aqueduct is considerably more extensive and spreads into the greater part of one anterior 

 corpora quadrigemina, a portion of the other, and extends downwards in the middle line 

 in a triangular process between the two red nuclei. A second large irregular area is found 

 in the middle line at the point of emergence of the Illrd nerve : this area stretches upwards 

 into the ventricular portion of both red nuclei (fig. 162). 



On both sides a thin irregular patch occupies the greater portion of the claustrum and 

 extends into the grey matter of the convolutions of the island of Reil. Two small patches 

 are present in the parietal operculum of one side, and similar but more extensive areas on 

 the opposite side. The posterior horns of the lateral ventricle show a number of irregular 

 patches, which extend outwards into the adjoining white matter. On the right side this 

 area extends to involve the tapetum, inferior longitudinal fasciculus, and optic radiation 

 — all of which are also involved in a well-marked round area at the base of the calcarine 

 fissure. Within the calcarine fissure on this side two small areas are found extending from 

 the surface of the grey matter directly into the medullary ray. 



Optic Nerves and Chiasma (figs. 163-165). — Sections cut horizontally through the chiasma 



