MACEOMYELON OF MAMMALIA. 



85 



of grey matter called ( corpus dentatum.' The pons, fig. 60, 5, c, 

 by its prominence and antero-posterior extent, corresponds with 

 the great lateral developement of the cerebellum, e. 



When the prepyramids, fig. 55, /?, are divaricated in the 



human macromyelon, the 

 median fissure, which is 

 wider and shallower than 



55 



al 



Base of the Brain, 



Postpontal part of Macromyelon, 

 anterior or ventral aspect. 

 Man, xxxiti". 



that, c, below the decussation, shows the same cribriform cha- 

 racter of its f floor,' formed by the penetrating vessels from 

 the fold of pia mater which lined it. A further extent of 

 divarication shows transverse fibres uniting the halves of this part 

 of the macromyelon, and decussating with longitudinal fibres, as 

 in fig. 56. The section of the prepyramid on each side of a, fig. 

 57, shows its triangular figure and the restriction of grey matter 

 to the ' nuclei,' /*, s ; they are mainly composed of white longi- 

 tudinal fibres which enter the pons above its lower or peripheral 

 transverse fibres, and interlace with the fibres of a higher plane : 

 at the entry each pyramid is constricted, as at fig. 56, p, but soon 

 expands. The proportion of the decussating and non-decussating 

 tracts of the prepyramidal columns is shown in fig. 56, where p 

 is part of the right prepyramid cut across near the pons and 

 reflected to show the decussating fasciculus, d, and the non-decus- 

 sating fasciculus, n, continued through the pons, P: the decus- 



