The brain of Acipenser. 107 
what caudal to the cephalic end of the acusticum. More exactly, in 
a young Acipenser about 30 cm in length the nucleus is about 
1,4 mm long, its cephalic border lies about 0,4 mm caudal to the 
point of exit of the III nerve, and its caudal limit is about 0,8 mm 
cephalad from the point of exit of the motor V nerve. The nucleus 
therefore lies partly in the mid brain and partly in the medulla. 
The elements making up the nucleus are relatively large, larger than 
the measurements of the cell bodies would indicate. The cell bodies 
are usually stellate, but occasionally fusiform or pyramidal, and 
measure 10—24 by 16—32 u. In measuring these cells it is very 
difficult to decide where the limit between the cell body and the 
dendrites lies. The dendrites are very thick and grow smaller only 
very slowly as they leave the cell. In all cases I have taken the 
smallest possible measurements, considering as cell body only the 
collection of protoplasm immediately surrounding the nucleus. The 
dendrites are richly branched and expand widely in the lateral 
columns. The cells which lie near the middle line, ental to the 
fasciculus, send their dendrites mesially around the fasciculus and 
ventrad at either side of the ventral raphe, where they branch 
among the fibres of the bundles of MEYNERT as they emerge from 
cereb 
Bigs Er 
the decussation (Fig. H). The neurites usually arise from the base 
of one of the dendrites, sometimes from the cell body. They are 
medium-sized smooth fibres which give off no collaterals so far as 
