426 
pared for the beautiful simplicity of this connection in fishes. After 
the ventral peduncle fibres unite with the cells of the cortical portion 
of the hypoaria, other branches pass dorsad from the same cells and 
either directly or by means of a simple anastomosis connect with the 
enormous tripolar or multipolar cells of the medullary part of the 
hypoarium (fig. 3). These cells are the most perfect switch cells 
imaginable and unite crossing tracts. In this way an indirect cellular 
Fig. 3. Cells from the medullary portion of the hypoarium (nidulus niger). 
Fig. 4. Cells from the peripheral ventral part of the hypoaria showing connection 
with the tracts. 
communication is affected with the dorsal peduncular tract, while the 
fibres pass dorsad into the cerebellum. Thus we find in fishes by 
direct observation what has been postulated by MEYNERT as a phy- 
siological necessity. The dorsal or medullary part of the hypoaria 
separating the dorsal from the ventral peduncles of the cerebrum oc- 
cupies the position of the nidulus niger as identified by us in 
reptiles. From what has been said, the hypoaria can only be regard- 
ed as modified representatives of the pes pedunculi. 
7. Considerable attention has also been given to the tectum 
opticum with results which seem to be in the line of pro- 
gress. The descriptions usually given place the tectum beyond the 
reach of comparison with other parts of the brain. The connective 
elements especially seem to have been completely misunderstood. 
They consist primarily of a single layer of cylindrical cells extending 
