104 Comparative Neurology. [F ebruary, 
Each spinal ganglion segment presiding over a similar series 
would be thus represented: 
a 
While each and every ganglion preserves its primary projection 
functions, the commissures interrelate the systems and are them- 
selves projection fibers. _ 
The third system in this. diagram is incomplete in not being 
commissurally connected, hence it is but.a ganglionic (interverte- 
bral) swelling upon the secondary spinal afferent nerves, and 
attains its complete functional character within the cranium only. 
In Trigla adriatica the brain and dorsum of the cord are marked 
by a double chain of well-developed tubercles on the secondary nerves 
just as they enter the cord. These ganglionic enlargements are exact 
reproductions of the cerebellar and cerebral enlargements, en chate- 
laine. hese intervertebral ganglia constitute the third system, the 
difference between the spinal ganglia and those above being that 
the latter are commissurally united to one another, and in higher 
Vertebrata fused longitudinally. 
The vermis of the cerebellum is probably a mere commissure 
compounded of different segmental heights, for the transverse 
striations are pronounced in birds and some reptiles. 
According to Owen, the cerebellum (vermis) retains its embry- 
onic form of a simple commissural bridge or fold in the parasitic 
suctorial Cyclostomes and sturgeon, and in the almost finless 
Lepidosiren, while the cerebellum (still vermis, because centrally 
placed) is highly developed in the sharks. In the saw fish it even 
rests upon the “ cerebrum.” 
The first well-marked posterior ganglionary mass which in 
higher Vertebrata becomes a portion of the cerebellum, is the 
vagus tubercle, placed posterior to and below the “cerebellum” - 
of the fox shark. It might be safe to assume that subsequently 
