The brain of Acipenser. 131 
cells which I have described above as constituting the end-nucleus 
of these bundles (page 106). 
The course of these bundles through the ansulate commissure 
and their decussation is exceedingly complicated and the study is 
rendered difficult in the last degree by the elements of the commissure 
and other bundles which are mingled with these. Since the de- 
scription here given is new, I shall describe in detail the appearance 
of the bundles at every part of their course as seen in section in 
different planes. 
In sagittal sections the separation of the fine fibres from the 
coarse is very clear. A few fibres of finer calibre seem to accom- 
pany the coarser, and indeed, there is no sharp distinction between 
fine and coarse fibres, the two graduating into one another. It is 
fair, however, to speak of that part which probably has its ending in 
the cerebellum and includes most of the fine fibres, as the fine- 
fibred portion. This portion continues on the ventral surface of the 
medulla to about the caudal border of the ansulate commissure 
without its fibres showing end branches or collaterals. The bundle 
is gradually lost to view in sagittal sections, owing to its fibres 
turning laterally. 
The ansulate commissure appears in sagittal section somewhat 
retort-shaped, its cephalic border being very thick and reaching 
nearly to the ventral surface of the brain. The area ventral to the 
caudal, broader, part of the commissure is known as the corpus 
interpedunculare. The coarse fibres of MEYNERT’s bundle pierce the 
cephalo-ventral part of the commissure and enter the corpus inter- 
pedunculare. Here little more is to be seen in sagittal sections than 
an enormous mass of densely packed nerve twigs and, near the 
median plane, a great many fibres running dorsally over the ental 
surface of the fasciculus longitudinalis posterior. The mass of nerve 
twigs is seen to be formed in large part by the end-branches of 
a large bundle of very fine fibres which comes from the medulla 
(bundle 2). 
In horizontal sections the course of the fine-fibred portion is 
clearly seen. The fibres cross at an acute angle beneath the ansulate 
commissure, the greater part of the decussation taking place ventral 
to the cephalic part of the commissure. A drawing from such a 
section was given in an earlier paper (98a, fig. 5) and Phots. 54 
and 55 accompanying this paper are taken from the same and an 
adjacent section. Many fibres turn laterad and do not decussate. 
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