Houser, Zhe Neurones of a Selachian. 11g 
proves to be. We have seen that the granular neurones con- 
tribute their axones toa series of fibres passing horizontally 
through a row of spreading PURKINJE dendrites; that the neu- 
rones of the molecular layer are themselves radiately connect- 
ing paths; and, finally, that the incoming nerve-fibres, those 
arising outside the cerebellum, end, some in the granular layer, 
others taking a longer course into the molecular layer. These 
several elements evidently have no other purpose than the 
bringing of all incoming impressions, through one path or an- 
other, to bear upon the neurones of PurkinjE. The great 
spreading top of a PuRKINJE cell is obviously a device for pro- 
viding a large receptive surface for such impressions, while the 
many thorn-like gemmules with which the dendrites are studded 
serve asa yet greater extension of that surface, or, perhaps, 
make one which is more readily impressed. The axone of the 
cell takes a more or less direct course out of the cerebellum, 
carrying the resultant of the nervous interactions to the proper 
point for ultimate distribution. If it is the purpose of the 
whole series of cerebellar elements to provide a central mechan- 
ism of equilibration, then the neurone of PURKINJE is certainly 
the centre of that mechanism. The various nerve-fibres sweep- 
ing into the cerebellum may terminate in several ways and at 
diverse levels of the organ, but everywhere there are devices 
for connecting them physiologically with the neurones of Pur- 
KINJE, which receive all and preside over all. 
The researches of LEE ('92, ’93, ’94, ’98). upon equilibra- 
tion in fishes have shown with what nice discrimination these 
aquatic animals balance themselves, devoid, as they are, of 
many sources of impressions possessed by terrestrial vertebrates. 
Doubtless a large number of equilibrial impressions are derived 
from the visual mechanism of the fish. Axones from the roof- 
nucleus of the midbrain pass backward into the cerebellum; 
and it will be shown in Subsection VI that there is a most inti- 
mate association between the roof-nucleus and optic termina- 
tions. Another source of equilibrial impressions is to be found 
in the fins and body musculature, entering the cerebellum 
through the tractus cerebello-spinalis. But the work of LEE 
