Houser, The Neurones of a Selachian. IOI 
each is the equivalent in every way of the element bearing such 
a name from the cerebellum. 
a. Molecular and Granular Neurones.—The molecular and 
the granular neurones do not call for any extended description 
here, since they are directly comparable with the cerebellar 
representatives described at length in Section V. 
The molecular neurones are the most numerous of the 
three varieties peculiar to the tuberculum acusticum. They are 
found scattered throughout the molecular layer, most abun- 
dantly in the deeper levels. Each has the characteristically 
small cell-body with slender dendrites radiating from it. 
The granular neurones are far less numerous. They lie 
just within the base of the molecular layer, but there are not 
enough of them to forma distinct zone. Stained with methylen- 
blue, they exhibit the typical dense nuclear structure and the 
small amount of cytoplasm. 
b. Purkinje Neurones.—The phylogenetic interest attaching 
to the presence in the oblongata of these elements calls for 
more special notice. The PurRKINJE neurones of the tubercu- 
lum acusticum are not disposed in any regular order. They . 
lie scattered between the deeper molecular neurones, and they 
are also found among the granular neurones. Their dendrites 
are always directed toward the limitans externa, whatever the 
situation of the cell-body may be, although the exact course 
may be at a considerable angle to the perpendicular. The axone 
always passes inward. Refer to Fig. 2, @ a. 
The cell-body is slightly oval or even perfectly circular in 
outline (Fig. 7). The particular form assumed appears to be 
correlated with the position of the dendrites. The gnarled 
character of a dendrite is quite evident. There are three or 
four of them, terminating in blunt tips. A dendrite bears few 
branches, or none at all, and its surface is studded with numer- 
ous thorny gemmules of various sizes, some of them quite large. 
The axone arises from the internal border of the cell. It 
takes a ventral course through the intervening nervous tissue 
into a bundle of arcuate fibres. Its ultimate distribution has 
not been definitely followed. 
