The brain of Acipenser. 207 
much larger than the left and AHLBORN notes a difference in the 
arrangement of the fibres in the ganglia similar to that described 
above for Acipenser (page 110). He speaks also of a crossing of a 
part of the fibres of each bundle to the opposite side which does not 
exist in Acipenser. The manner of ending of these bundles in the 
base of the mid brain is interesting. Opposite the point of exit of 
the III nerve a part of the fibres decussate “und bildet hier einen 
asymmetrischen, eigenthiimlichen, hellen und äusserst feinkôrnigen 
Körper, welcher der Haubeneinschnürung direct aufgesetzt ist”. The 
remainder of the fibres continue on backward, one bundle on either 
side of the corpus interpedunculare, and gradually turn upward and 
inward, presumably to end deeper in the base of the brain. Im- 
mediately behind the corpus interpedunculare the bundles of the 
two sides approach one another, unite and continue for a short 
distance in the raphe, and finally end in a cone-shaped point. The 
corpus interpedunculare is thus embraced between the two bundles, 
but “ein Eintreten von Fasern des MEYNERT’schen Bündels in dieses 
Ganglion habe ich nicht beobachtet und halte es auch nicht fir 
wahrscheinlich”. 
In this description AHLBORN really gives no indication of the 
actual place of ending of the bundles of MEYNERT. I am not sure 
that work of this kind can be relied upon for any certain results in 
so enormously complicated a region as this. Ordinary histological 
sections unaided by GoLGI series are almost or wholly worthless 
for the study of the ending of these bundles. Indeed, after a com- 
plete study with GoLa&r series it is extremely difficult in haemato- 
xylin sections even to recognize the limits of the various structures 
involved. As AHLBORN was the first to find the bundles in question 
extending caudally beyond the corpus interpedunculare, it is worth 
while to examine his description. In Petromyzon the decussation, 
which involves the greater part of the fibres, takes place in front of 
the corpus interpedunculare, in Acipenser by far the greater part of 
the decussation lies in the corpus. AHLBORN could not trace the 
fibres beyond their decussation and leaves it to be inferred that they 
end in his lightly staining body. Of the fibres which do not decus- 
sate he finds many at the sides of the corpus turning upward and 
inward, presumably to end in deeper parts of the base of the brain. 
In Acipenser it is the decussating fibres which turn upward and 
inward, after decussation. In Petromyzon the direct fibres continue 
in a mid ventral position until they gradually disperse to their endings. 
