UNILATERAL CEREBELLAR AGENESIA 369 
be assumed that some of the fibers of the medial fillet terminate 
in the superior colliculus—which is disputed by some—the 
atrophy or agenesia of the latter might account for this. Im- 
perfections in the series did not permit this point being fully 
investigated. 
Sections further cephalad indicate that the fibers of the left 
juxta-restiform body, connecting the vestibular area with the 
vermis cerebelli are reduced in number, though present. De- 
fects in the sections prevented their being followed into the 
cerebellum. | 
A section just caudal to the exit of the left trigeminus (fig. 12) 
shows the position and maximum size of the left, atrophic; nucleus 
dentatus. Dorsal to it is a rounded mass of abnormal cerebellar 
cortex (compare fig. 5, 1). 
Figure 12 also shows the abnormal features of the pons. On 
the left the pons consists almost entirely of gray, the pontile 
nuclei, through which the longitudinal bundles of the pyramid 
are proceeding. From these nuclei transverse pontile fibers 
pass across to the right and accumulate on the extreme right as 
the right brachium pontis or right middle cerebellar peduncle. 
On the other hand, the right pontile nuclei are almost entirely 
absent and the same is true of the left middle peduncle, there 
being only a lght-staining mass containing scattered fibers. 
While it is obvious that this shows the ponto-cerebellar con- 
nection to be mainly a crossed one, the possibility of there being 
a small minority of uncrossed fibers cannot be logically excluded. 
It will be noticed also (fig. 12) that the ventral part of the 
tegmentum, laterally to the left medial fillet, contains masses 
of gray not present here nor further cephalad on the right and 
not usually found so extensively here. Nerve cells of normal 
appearance are present in them. It is suggested that the left 
pontile nuclei are somewhat hypertrophic and have invaded the 
tegmentum. Among the ordinary transverse fibers decussating 
through the medial fillets are bundles of fibers resembling the 
transverse pontile fibers in stain. They are found in this and 
other sections of about this level on both sides. It is difficult 
to trace their origin and destination but they appear to arise 
