The brain of Acipenser. 133 
masses of nerve twigs at either side of the decussation. There is 
in most sections some appearance of fibres or collateral branches 
turning to re-cross the middle line, but always on close examination 
I have found these fibres only turning back slightly and then running 
dorsad. After the most painstaking efforts I have been unable to 
find in any case either fibres or their collaterals re-crossing in the 
decussation. Both the coarse fibres and the fine branches into 
which they divide turn abruptly dorsad after decussating and form 
a bundle which runs around the ental surface of the fasciculus longi- 
tudinalis posterior. The conspicuous bundle in this position in 
frontal sections is formed in part also by the dendrites of cells which 
lie next the cavity around the fasciculus. These dendrites branch 
in the lateral part of the decussation and help to form the mass of 
nerve twigs found there. Here without doubt the dendrites come 
into functional relations with the fibres or their collaterals. The 
statement of the course of the fibres through the decussation does not 
rest alone on tracing the bundles en masse, but I have been fortunate 
enough to find single sections in which I have traced several fibres 
individually from the bundles of MEYNERT before decussation, through 
the decussation and into the dorsally directed bundle. This bundle 
courses around the fasciculus and breaks up in the nucleus which 
has heen described in a previous section. 
I have mentioned in describing sagittal sections that the dense 
mass of nerve twigs at either side of the decussation is formed in 
large part by fine fibres coming from the medulla. In frontal 
sections these fine fibres are recognized and they, too, cross the 
middle line among the decussating fibres of MEYNERT’s bundles. 
After decussating these fine fibres run with the fibres of MEYNERT’s 
bundles around the fasciculus to end in the same nucleus. All the 
fibres which enter this nucleus end by very fine branches which 
form an exceedingly intricate network about the bodies of the cells 
and the basal part of the dendrites. Beyond the caudal limit of 
the decussation of MEYNERT’s bundles the fine fibres from the 
medulla continue to decussate and end in this nucleus. It is the 
crossing of these fine fibres which appears in Phot. 54 caudal to 
the coarse decussation. I have been unable to determine the source 
of these fine fibres. In frontal sections the bundle can be traced 
caudally to about the level of the VIII nerve. The fibres gradually 
disappear among the medullated fibres of the ventral columns. 
