CRANIAL NERVES OF SILURUS AND MORMYRUS 35 
farther forward, however, much more than the medial lobe, 
and at the place where both lobes have fused with their contra- 
lateral structures the fusion of the lateral lobes lies dorsally of 
the fusion of the medial, forming the larger arch of the two. 
Both then continue into the cerebellum by a fusion of the crista 
cerebellaris with the molecular layer of the cerebellum. 
The relations as found in Mormyrus bear a great resemblance 
to those in Silurus in that here also the lobe of the posterior lateral 
nerve is by far the larger of the two. Since, however, both are 
hypertrophied in Mormyrus, the fusion of each with its contra- 
lateral formation—which fusion in Silurus occurs only in the 
more frontal sections—is present in Mormyrus over the whole 
extent of the lobes. And since the medial lobe (related to the 
anterior nerve) is entirely covered by the enormously increased 
lateral lobe, the entire center makes the impression of consisting 
of one tuberculum impar (ef. figure 6 of Silurus with figure 19 
of Mormyrus). 
The only differences between the two animals, consequently, 
are matters of degree, being: first, that in Mormyrus the dorsal 
fusion of the homologus lobes takes place over the whole extent 
of the formation; second, that the greater size of the lateral lobe 
(of the posterior nerve) as compared with the medial lobe (of 
the anterior nerve) is so much increased that it is not the medial 
lobe which extends farther caudad but the lateral one, and this 
overlies the former not only dorsally but also caudally; and third, 
the contribution of the nervus lateralis anterior to the lobe of 
the nervus lateralis posterior of Mormyrus is much larger than 
that of Silurus. 
It will appear in the following description that the secondary 
tract from these lobes, the fasciculus longitudinal lateralis, 
is correspondingly increased and that the midbrain nucleus of 
that tract, the torus semicircularis, is in turn connected with the 
valvula cerebelli, especially with its lateral lobes, the enlarge- 
ment of which thus depends on the lateralis systems and their 
secondary connections and not on the poorly developed taste 
nerves. 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 25, NO. 1 
