The brain of Acipenser. 173 
fibres agree with the internal arcuate fibres of human anatomy and 
may rightly be given that name here. Herrick also mentions a 
secondary bundle, mainly of uncrossed fibres, which runs to the 
cerebellum. I have not found this bundle in Acipenser. Other 
secondary fibres from the acusticum which run to the opposite side 
in a superficial position may be given the name of external arcuate 
fibres, although they reach the surface directly from the acusticum, 
instead of running by way of the raphe and ventral fissure as in 
human anatomy. Whether they are homologous with the external 
arcuate fibres of human anatomy will depend upon their destination, 
which I have been unable to make out. 
Morphological unity of dorsal horn, acusticum, 
and cerebellum. — The argument for this conception rests upon 
the close connection between these structures, their isolation from 
the lobus vagi, the comparison of the nerve elements in the several 
nuclei, and the connections of these nuclei with other parts of the 
brain by means of the neurites of their cells. The nucleus funiculi 
is the common nucleus for the spinal V and the dorsal tracts of the 
cord in all Vertebrates. Considering the nerves which end in this 
nucleus, two facts point to close connection with the acusticum. 
First, the spinal V is only a part of a large nerve, the remainder 
of which ends in the acusticum. Second, the lateral line and VIII 
nerves hold exactly the same relation to these two nuclei. The 
nucleus funiculi and the acusticum both serve as common end-nuclei 
for parts of all three nerves, V — VIII — lateral line. On the 
other hand, turning to the connections with the cerebellum, we find 
all the cutaneous nerves ending partly in the cerebellum also. 
Finally, I have shown that the acusticum and cerebellum are di- 
rectly continuous and that no dividing line can be recognized. This 
has been stated also by MAYSER, GORONOWITSCH, STRONG, and 
KinGsBury, although not based by these authors on minute study 
by modern methods. 
In contrast to the close connection of these nuclei with one 
another stands the marked isolation of all of them from the lobus 
vagi. No author has described anything to indicate continuity, si- 
milarity of internal structure, or community of function between the 
acusticum and the vagus lobe. GORONOWITSCH (’96, p. 7) indeed 
says that in ordinary histological preparations the „Lobus trigimini” 
(= part of acusticum) has an appearance very similar to that of the 
lobus vagi. That this is certainly very wide of the mark must be 
