112 JouRNAL OF CoMPARATIVE NEUROLOGY. 
tween. the nerve-fibres. The external morphology of one of 
these neurones is represented in Fig. 14. From a small, almost 
perfectly spherical cell-body, three or four dendrites radiate, 
branching in what is an approach to a dichotomous manner. 
The dendrites are not thick at their bases and they become lost 
to view before proceeding far, owing to the fineness of the 
terminal twigs. The surface of a dendrite is almost perfectly 
smooth, there being only the faintest indication of gemmules, 
but there are small varicosities at irregular intervals which pro- 
duce slight variations in the thickness. 
The internal organization of the cell presents a large, 
rounded nucleus which is enveloped by a stratum of cytoplasm 
of no great thickness (Fig. 50). The cytoplasm contains tigroid 
_ substance distributed in granules of the most minute size, mere 
points even when highly magnified. The chromatin is distrib- 
uted along a linin reticulum of such fine mesh that the nucleus 
is thereby often made to appear almost perfectly black. There 
is a single nucleolus. 
In mammalian neurology, the molecular layer is known to 
have two varieties of cells: (1) stellate cells, the processes of 
which lie freely in the layer; and (2) basket cells, somewhat 
larger in size, occupying the deeper levels of the layer, and 
having their axones associated with each other in such a way as_ 
to form plexuses or baskets around the cell-bodies of the Pur- 
KINJE neurones. ‘The latter type of cell is, of course, the more 
specialized of the two. It is therefore interesting to note that 
it is not represented in Mustelus, but that all of the molecular 
cells correspond, rather, to the stellate cells of higher verte- 
brates. Such a result is, however, to be expected in a brain of 
lower phylogenetic value. 
3. The Granular Layer. 
The granular layer lies internal to both the molecular layer 
and the neurones of Purkinje. It is somewhat irregular in its. 
distribution. At many places it is twice as thick as the molec- 
ular layer, notably at the summits of the great folds; while it 
tends to decrease in extent as the bottom of a fold is reached. 
