Houser, The Neurones of a Selachian. 1 a 
The molecular layer is characterized by the predominance 
of fibrous elements and the fewness of nerve-cells. In contrast 
with the mass of densely-packed, conspicuous cells of the gran- 
ular layer, the outer region presented hardly more than a 
minutely punctate appearance to the earlier investigators who 
had recourse to nothing more differential than the general stains 
in use at that time. Hence molecular seemed an appropriate 
descriptive term for this layer. 
Through the use of modern methods, we find the molecular 
layer to have a few proper neurones of small size, but the great 
mass of substance consists of fibrous material, between the 
parts of which the nerve-cells are intercalated. But, it is cer- 
tainly a fact worthy of mention, the fibrous constituents of the 
layer do not have their origin there, penetrating it, rather, from 
deeper levels. The dendrites of the PuRKINJE neurones, and 
the processes from the neurogliar cells comprise one great class 
of constituents. These take a course perpendicular to the sur- 
face and cause the vertical striation which is so marked a fea- 
ture of the region. Then, too, the neurones of the granular 
layer send their axones outward into the molecular layer for 
a T-shaped division, each thus giving origin to a pair of fibres. 
These branches take a course across the sagittal plane of the 
cerebellum, parallel at once with the limitans externa and the 
lateral surface of a fold. To the presence of these fibres, cut 
across in such numbers in a sagittal section of the cerebellum, 
the characteristically punctate appearance of the molecular layer 
is chiefly due. Finally, it should also be noted, there are 
numerous terminations in the molecular layer of nerve-fibres 
which have entered the cerebellum from some other region of 
the nervous system. Such terminating fibres branch so as to 
distribute the endings over a considerable superficial area. 
It will thus be seen that the molecular layer is really a 
tangle of nervous tissue, a series of paths where many associa- 
tions may be formed. This topic will be discussed more at 
length in the fifth subsection. 
The neurones proper to the molecular layer are, as APES abe 
noted, but few in number, and those present are scattered be- 
