12 J. B. JOHNSTON, 
of the dendrites. The tract cells are smaller than the motor cells, 
the limit between the cell body and the dendrites is more sharply 
marked, and the dendrites have not so great an expansion or so 
profuse a branching as those of the motor cells. The neurites arise 
most often from one of the dendrites, sometimes at a considerable 
distance from the cell-body, pass ventrad or laterad and turn to 
become fibres of the longitudinal tracts. In most cases the neurites 
can be traced for only a very short distance in either frontal or 
longitudinal sections but I have no doubt that their fate is the same 
as that of neurites of tract cells in the cord, as described by 
LENHOSSEK (92), MARTIN (95), Van GEHUCHTEN (’95), AICHEL (95), 
and RETZIUS (95) in embryos of Selachians and Teleosts. 
The commissural cells are in every way like the tract cells, 
except that their neurites cross the ventral raphe to enter the tracts 
of the opposite side. 
Sp.V.. 
F 
N 
° 
li N = 7s y 
olive "NX °o ff °°0 
neurite IN % oo 2 
N Be eee 
ie 
° © off Oro = £ 3 
‘fibre from sp.V. 
Fig. A+). 
The lower olive (Fig. A). Immediately surrounding the cephalic 
two rootlets of the XII. nerve is a small group of fusiform cells arranged 
with their long axes parallel with the surface. The cells measure 8—16 
by 16—32 u. They have two or three dendrites, usually disposed 
transversely. The neurites arise either from the cell bodies or from the 
dendrites, cross the ventral raphe, course around the lateral surface, 
send collaterals into and finally break up among the lateral tracts. 
1) For explanation of textfigures see page 251. 
