124 
Ulinski 
VENTRICLE 
40p 
I ^ 
Figure 3. Zone A neurons (1 and 2) are shown as they appear in rapid Golgi preparations. Their dendrites 
extend down into zone B. Several ependymal cells are also shown. These bear long processes which extend 
radially through ADVR. Only the proximal shafts of these processes are shown. 
VENTRICLE 
Figure 4. Zone B neurons are shown as they appear in rapid Golgi preparations. Their dendrites extend 
into both zones A and B bearing a high density of dendritic spines. Their axons extend primarily 
into zone A where they ramify concentric with the ventricle. A few zone B neurons (neuron 4) send their 
axons into zone C. 
Golgi preparations (Fig. 7). Type 1 axons 
are about 2fi in caliber and proceed recti- 
linearly into ADVR, bearing thin collaterals 
which have small varicosities about 3 /a long. 
They are confined principally to zones C 
and D. Type 3 axons are thin throughout 
their course and bear small varicosities. They 
extend radially through zones C and D and 
turn to run concentric with the ventricle in 
zone B. Figure 8 shows a zone B neuron 
intersecting the trajectories of many type 3 
axons. They are positioned so that an indi- 
vidual fiber can contact several dendrites on 
the same neuron and then continue on to 
affect many other zone B neurons. Type 2 
axons can also be defined ; they are the axons 
of zone B neurons (Ulinski, 1976a). 
Some information about the origins of type 
