423 
campus of mammals so far as homologies can prevail under such 
diverse conditions. 
3. The fibres of the ventral peduncle of the cerebrum arise 
in the processes of the cells forming the frontal and lateral lobes, 
i.e. the anterior or cephalo-lateral parts of the axial lobe. The fibres 
pass with those of the dorsal peduncle into the thalamus beyond the 
corpus geniculatum externum, after which they are suddenly flexed 
ventro-laterad into the hypoaria. There they divide into radial bund- 
les which occupy the ventral aspects of the hypoaria and terminate 
in curious bifid cells of its peripheral portions. None of these fibres 
pass directly into the medulla. Fig. 4 illustrates the form of the 
peripheral cells of the hypoarium. 
4. The dorsal peduncle is composed of fibres arising in the cells 
of the caudo-lateral and dorsal parts of the axial lobe. The actual 
connection with the apex-process of the cells can be seen in sections 
properly orientated and followed into the peduncles. These peduncles 
remain rather distinct from the ventral and pass directly caudad in 
the thalamus, receive fibres from the geniculatum, and divide into 
numerous bundles as they pass through a dense nidulus in the base 
of the thalamus above the cinereum (nidulus subthalamicus). 
From this region these fibres collect about the „nucleus ro- 
tundus“, Fritsch, in the most complex manner and anastomoses 
are formed with numerous other regions. Most important of these are 
connections with the ventral peduncles indirectly in the medullary 
nidulus of the hypoaria (nidulus niger) and with the dorsal cell- 
clustres of the thalamus. From this point the dorsal peduncles pass 
into the medulla, reaching its dorso-lateral tracts. 
5. The nucleus rotundus has hitherto baffled examination. 
It is now possible to explain its structure. It was described by Pro- 
fessor FRITSCH as composed of irregular protoplasmic lumps of inde- 
finite character and adds „Bei solchem Verhalten ist es erklärlich, 
daß man nur schwer sich eine feste Vorstellung davon bilden kann, 
in welcher Weise die in Rede stehenden Organe zusammengesetzt 
sind.“ 
The accompanying figure (fig. 1) shows that with other methods 
it is possible to resolve this nebula. In fact, the comparison with a 
nebula is not far from happy, for the ill-defined clumps resolve them- 
selves into rosette-like clustres of cells which are surrounded by suffu- 
sed material. In the large series of fish brains at disposal a great 
diversity is encountered in the form and structure of the body, but 
it always remains essentially the same. In some cases (and generally 
