The brain of Acipenser. 241 
11) In Mammals (Casa) and fishes (HERRICK, JOHNSTON) the 
fasciculus communis is not confined to the medulla. In both these 
classes and probably in all Vertebrates there is a median nucleus 
in connection with the commissura infima Halleri and a cervical 
continuation of the fasciculus communis which seems to be con- 
stituted of direct root fibres of the VII, IX or X nerves. This 
cervical bundle is related to the central grey dorsal to the canalis 
centralis and its fibres probably end in relation with cells in the 
region corresponding to CLARKE’s column or the dorsal commissure 
in Mammals. 
12) The lobus vagi is constituted of cells of the II type which 
receive the endings of the sensory fibres, and of cells which send 
their neurites into the secondary vagus tract. 
13) The nucleus of the secondary vagus tract at the cephalic 
end of the medulla, besides giving rise to a commissure through the 
cerebellum, sends fibres ventrad which may either make connections 
with motor nuclei or run to some nucleus farther forward. 
1¢) The tectum opticum is a primary optic center and a se- 
condary center for cutaneous sense organs and the ear. The tectum 
contains cells of three main kinds. Two of these, the cells with 
short neurites and those whose neurites go out to the retina, are 
directly related to the optic tracts. The third receives secondary 
impulses both from the cells with short neurites and from the 
secondary acustic and cutaneous sensory tracts. The cells of this 
third group send their neurites to other parts of the brain, lobi in- 
feriores, cerebellum, or medulla. They are of various forms, but it 
is not known whether they can be divided into distinct classes ac- 
cording to the destinations of their neurites. 
15) The torus longitudinalis is probably to be compared with 
typical parts of the tectum. The torus semicircularis also belongs 
to the tectum (secondary nucleus) and not to the central grey. 
16) The fibre tracts leaving the tectum set up connections 
1) directly with the motor nuclei of the medulla (and cord?), or 
indirectly by means of the commissure and tract cells; 2) with the 
cerebellum; and 3) with the lobi inferiores. The tracts to the lobi 
inferiores are made up in part of collaterals from the fibres of the 
tracts to the medulla. 
17) The ganglia habenulae have in the main the same structure 
and relations as in other Vertebrates. I have described a new 
nucleus of ending for the bundles of MEYNERT, situated adjacent to 
Zool, Jahrb. XV. Abth. f. Morph. 16 
