The brain of Acipenser. 217 
ending in the nucleus trapezius of WESTPHAL and MUNZER- WIENER, 
lateral to the ganglion interpedunculare. 
It is evident that the bundles of MEYNERT have not that de- 
gree of constance in their relations which EDINGER attributed to 
them in 1896 (Vorlesungen, p. 123). The investigations by the 
GouLGI method upon Selachians, Teleosts, frog, and Reptiles have 
given entirely consistent results. But the conditions in Acipenser 
and the pigeon make it necessary to review the whole subject of the 
structure and function of the habenular apparatus. The constance 
of its connection with the olfactory centers suggests that the ganglion 
habenulae is a part of the olfactory apparatus. That this can not 
be its only significance is pointed out by EDINGER (’96b, p. 124), 
since it is present in Mammals which have scarcely any olfactory 
nerves. Other fibres enter the ganglia in some Vertebrates and 
further investigation of such fibres must be made before any final 
conclusions can be drawn regarding the significance of these ganglia. 
I have shown that fibres from the pineal gland enter the ganglia in 
Acipenser. However important the pineal organ may have been in 
early Vertebrates, it can scarcely be thought that it exercises any 
considerable influence on the ganglia habenulae in recent forms. 
EDINGER (92) mentions bundles connecting the ganglia habenulae 
in Selachians with the thalamus and tectum, as well as with the 
fore brain. I have heen unable to find these bundles in Acipenser. 
EDINGER (99) also describes in the Reptiles a medullated bundle 
from the commissura habenularis to the epiphysis, and two habenular 
tracts not before described, a tractus habenulo-diencephalicus and 
a tractus habenulo-periventricularis. Whether these are present in 
higher Vertebrates and form important parts of the habenular ap- 
paratus, awaits further investigation. In Mammals KÔLLIKER finds 
a large part of the fibres of the stria medullaris ending in the 
ganglia habenulae. These fibres probably come from the 1) Ammons- 
horn via fornix, 2) ganglion basale and neighboring ganglionic 
masses, 3) stratum zonale and the interior of the thalamus, including 
probably fibres of the optic nerve, and 4) from the nucleus inter- 
medius (KÖLLIKER). 
From these facts the conclusion may be drawn that in the 
_ lower Vertebrates the ganglion habenulae belongs to the central 
mechanism of the parietal eye and the olfactory organ (the relation 
with the parietal eye being the older ?), and that in the higher Ver- 
tebrates, beginning with the Reptiles, it has come to serve as a part 
17 
