The brain of Acipenser. 105 
inferiores, cerebellum or medulla, and it is worthy of note that the 
zone of expansion of the dendrites of these cells corresponds in a 
general way to the zone of expansion of the neurites of the cells 
of type A. 
Type E: superficial fusiform cells (Fig. F). In the outermost 
layer of the tectum are a considerable number of fusiform cells with 
two long dendrites running parallel with the surface. These cells 
with their dendrites lie among the fibres of the superficial fibre 
zone. The cell bodies measure 8—-16 by 12—32 u, the dendrites 
are long and meagerly branched. The neurite arises from one of 
the dendrites at some distance from the cell body, or the dendrite 
becomes transformed into a slender smooth fibre, which is the neurite. 
In all cases where I have found the neurite, it arises in one of these 
ways from that dendrite which is directed laterally, and the neurite 
runs laterally and ventrally with the tracts to other parts of the 
brain. 
Cells of doubtful character. I have found a few stellate cells 
situated in the middle third of the tectum whose dendrites expand 
at the same level as those of the cells of the type C, but are neither 
thick nor richly branched. The cell bodies measure 12—18 by 
14—20 uw. The neurites enter the middle zone of fibres. I have found 
a single cell situated at the surface of the tectum near its lateral 
border which has a pyramidal body and a single dendrite directed 
centrally. The neurite joins the superficial fibre layer. Both of 
these cells correspond to these of type D in the disposition of their 
dendrites and in the course of their neurites. 
In drawing Fig. F I have tried to represent a typical section 
of the tectum by drawing examples of all the forms of cells from 
different series of sections. 
Torus semicircularis Halleri. — The cells of the torus 
are fusiform and are arranged in an inner cellular zone with their 
dendrites directed radially outward. They measure 8—24 by 16—32 u 
They are thus placed similarly to the cells A and B of the tectum, 
but they are larger and with respect to their neurites they are to 
be classed with the cells D. The neurites arise from the basal part 
of the dendrites and enter at once the tractus tecto-bulbaris. The 
greater number of fibres run in the crossed tract through the com- 
missura ansulata (see page 125 below). 
Nucleus magnocellularis. — In Acipenser as in other 
lower Vertebrates there is found in the cephalic part of the tectum, 
