96 

 frorn a polygoa^l call-body. The office of this neurone may be 

 to bring the collateral branches of the other ani more numer- 

 ous nery^oas elements into relationship. Pig. 54 shows a group 

 of five of these cells, an unusually large number to find in so 

 limitei a fieli. 



2. The Central r;rau Hatter. 

 The aqueiuct of Sylvius is surrouniel by a layer or nerve- 

 cells and nerve-fibres representing the most archaic part of the 

 brain, and quite properly termed the central gray matter (Pigs. 

 20 and 21, c.g.ii.). The greater part of this nervous matter 

 has been supplanted or overshado/fel functionally by more recent 

 aiditions upon its outer surface, but certain nail defined 

 groups of neurones have retained their pristine importance 

 through the character of their ultimate connections. These 

 are, respectively, the roof-nucleus, and the nuclei of the 

 oculomotorius and the trochlearis. 



a. The Roof-Huol eu3 . -- This is a collection of very large 

 neurones lying in the roof of the aqueduct of Sylvius between 

 the ependyma anl the dorsal commissure of the stratum medullare 

 profundum. The group has a considerable longitudinal exten- 

 sion, reaching from the anterior end of the optic lobes to near 

 the juncture with the cerebellu-n. It is broken into two later- 

 al halves by the median line. Pig,2'),r.n. exhibits the entire 



