The brain of Acipenser. 87 
and take a strong impregnation which serves to distinguish them 
sharply from the medullated fibres with which they are mingled. 
Following this bundle caudally from the middle of the vagus lobe, 
it is found to grow constantly and gradually smaller until near the 
caudal end of the medulla, then it continues of about the same size 
down into the cord, and at the end of the series of sections it again 
decreases in size and is apparently about to disappear. Its decrease 
caudally is due to the fact that a much smaller number of fibres 
turn backward than forward and also to the fact that the fibres end 
in relation with the tract and commissural cells of the lateral columns. 
The neurites in the caudal end of the vagus lobe run into various 
parts of the lateral columns without joining this tract. The fibres 
which turn forward form a conspicuous but diffuse tract which con- 
tinues to the cephalic end of the medulla and ends by profuse 
branching in a large nucleus described by MAYSER under the name 
of “Rindenknoten”. For this tract and nucleus I shall use the names 
secondary vagus tract and nucleus. The position of the 
tract and nucleus is shown in the trace drawings accompanying 
(Phots. 8—16). 
The nucleus lies in close contact with the ventral and cephalic 
surface of the acusticum and the nucleus of the ascending V tract, 
at the junction of those structures with the cerebellum. The fine 
fibres of the tract as they subdivide and enter the nucleus form a 
compact layer around the lateral and cephalic surfaces of the nucleus, 
somewhat in the form of the bowl of a spoon, the handle of which 
is represented by the tract itself. The end-branching is so profuse 
and the fibres are so heavily impregnated in all my preparations 
that the study of the cells and their neurites has not been wholly 
satisfactory. As shown by both haematoxylin and GOLGI sections, 
the nuclei of the two sides are connected by three commissures 
(sometimes four) of non-medullated fibres passing through the ventral 
part of the body of the cerebellum (Phots. 16, 17). These will be 
further described directly. 
The most of the cells of the nucleus are small, measuring 12—18 
by 12—32 u. Their dendrites ramify among the end-branches of 
the fibres of the secondary vagus tract and their neurites are usually 
lost among these fibres, it being impossible to trace them far from 
their cells owing to their sinuous course and the density of the 
fibre mass. In the dorsal part of the nucleus the most of the 
neurites are directed toward the commissures. Other cells send their 
