758 
MR. A. SANDERS ON THE ANATOMY OF THE 
the divergence of the two branches ; at the external edge the fibres are sometimes 
seen to form loops turning back towards the centre. 
The Purkinje cells in Teleostei differ from those in the cerebellum of Mammalia in 
being less complicated, inasmuch as their thick processes do not divide into two 
branches, giving off a forest of straight fibres, but continue as a single trunk for some 
distance, and enter the external layer before dividing, and that only dichotomously. 
Moreover, they are placed with their long axis parallel to the long axis of the cere- 
bellum, instead of transversely to that axis, as in Mammalia. They resemble, in fact, 
the cells of the corresponding layer in the cerebellum of the newly-born infant in the 
simplicity of the arrangement of their prolongations. 
The third layer (fig. 23, e.) is composed of cells of extreme minuteness, which 
possess a nucleus, a nucleolus, and a small quantity of protoplasm. They are usually 
pear-shaped, and from the pointed end an extremely fine fibre proceeds ; which fibre, 
with those of the other cells in this layer, join together in a network which forms 
ramifications in the neuroglia of this stratum. Occasionally some of these cells are 
seen to be attached by their points to the side of a fibrilla. 
The theory I adopt as to the arrangement of the elements of the cerebellum is this : 
The broad processes of the cells of Purkinje divide continuously until they arrive near 
to the external edge, by which time they have become extremely fine ; they then turn 
back, and form a network in this layer, and, passing between the cells of Purkinje, 
finally join the corpuscles of the third layer, uniting them together in an inextricable 
network. 
The above theory is based on the following circumstances. In teased-out prepa- 
rations, the broad fibres of the Purkinje cells are found to be covered by coarse 
granules, which are attached to them at a certain distance from the cell, at points 
nearer to 'which they are smooth. These granules resemble those found in the 
neuroglia of the external layer. The cells of the third layer are seen, when teased out, 
to he united together by fine fibres, which are quite smooth, having no attached gra- 
nules. Thus it is found that the characteristic elements of the external layer are 
fibres to which coarse granules are attached, giving them a granulated appearance ; 
while the third layer is distinguished by cells the fibrils of which are smooth. 
In some preparations of teased-out Purkinje cells the broad fibre is seen to become 
more and more decreased in size, and the finest fibres have granules attached. On 
the other hand, preparations of the cells of the third layer have been made in which 
fibrils longer than usual have been preserved unbroken ; these, smooth near their 
origin, have become covered with granules, resembling those of the first layer, at a 
greater or less distance from the cell. From this it may be inferred that the latter fibres 
pass from the third layer into the first. But on the above supposition, what becomes 
of the fine fibres of the Purkinje cells? Gerlach (71) made out that they joined 
the cells and network of the third layer, which if the above description be anywhere 
near the truth cannot be the case, and his opinion is not confirmed by Deiters (73). 
