UNILATERAL CEREBELLAR AGENESIA Sal 
by the nearly complete absence of the left superior cerebellar 
peduncle and perhaps in some measure to the practical absence 
of the right central tegmental tract. 
The left mesencephalic root of the trigeminus is only about 
half the size of the right. It is difficult to tell, on account of 
deficiencies in the series, whether this is connected with the 
defect of the left superior colliculus. 
In figure 15 an interesting asymmetrical bundle is seen on the 
right issuing from the central gray and passing ventrally in the 
raphé. Its fibers could not be traced with certainty to the 
perpendicular pontile fibers but this connection seemed probable. 
From this bundle while in the central gray a small bundle passes 
laterally into the reticular formation. In figure 17 another 
bundle is seen on the left passing from central gray into reticular 
formation. It is connected with a snarl of fibers seen in the 
central gray, apparently an abnormal condensation or local 
increase in the plexus of medullated fibers normally found in the 
central gray. Another similar appearance is noted below 
(p. 372). A possible cause for these phenomena that suggests 
itself is that they are due to the irritative effects of an ependymitis 
at an early period of development. The other bundles in the 
central gray noted above are perhaps similar in character. Some 
of these bundles may be more an increase of fibers normally 
present than entirely new appearances. In this case they 
might throw some light on the rather obscure connections of the 
central gray. 
In comparing the pons at various levels it will be noted 
that there is a steady increase in the longitudinal fibers in the 
left pons. At the lowest level of the pons the longitudinal 
fibers (here almost exclusively pyramidal fibers) are about equal 
on the two sides. At the upper levels of the pons the longi- 
tudinal fibers on the left are, as far as can be made out, about 
double those on the right. This discrepancy is not so apparent 
on casual inspection on account of the greater number of trans- 
verse pontile fibers on the right and the great number of middle 
peduncular fibers accumulated on the lateral border. 
