A FISH BRAIN FROM THE COAL MEASURES 153 
teleosts,”’ then this region contains the ‘olfactory tracts,’ or crura 
olfactoria. The small size of the olfactory lobe suggests that 
the olfactory organs were not highly developed; it is, therefore, 
not improbable that the region designated ‘olfactory tract’ is 
really the slender olfactory bulb. This region is, unfortunately, 
only partially preserved in all the specimens studied, but the 
portion preserved is very interesting. Doubtless just anterior to 
the broken end (fig. 15) the tracts separated into the olfactory 
nerves, as in Rhadinichthys (fig. 4). A cross section of the ol- 
factory bulbs (or tracts) is readily obtained and the structure 
involved is shown in figure 7. The cavity of the rhinocoele is 
preserved by the formation of crystals around it. Its form and 
the fact that the surrounding wall is massive on all sides suggest 
that at the site of the section we are dealing with olfactory bulb 
rather than with olfactory crus. The cross section shows that 
the two bulbs are apparently fused in the medial plane, as in the 
frog; but it is impossible to determine whether this appearance 
is artificial or an expression of a real anatomical fusion. 
The larger brains of a fish from the Coal Measures are so 
distinct in some features as to be worthy of special consideration. 
One of them is figured in lateral view (fig. 9). The chief points 
of interest are readily observed from an examination of this 
figure. The olfactory tracts are quite similar in the two types of 
brains. It will be seen that the olfactory lobes and the thalamus 
are much smaller in proportion to the size of the brain than in 
the brains shown in figures 15 and 16. The optic lobes, on the 
other hand are very much larger and constitute by far the greater 
part of the brain. There is no median sulcus dividing the lobes 
as in the smaller brains. Its place is taken by a well marked 
ridge. There is thus no sure indication of that organ which is 
tentatively determined as the dorsal blood vessel, though pos- 
sibly the ridge is formed by the meninges enclosing such a vessel 
and strongly compressed laterally. The lateral lobes of the cere- 
bellum are very slightly developed and their median ends are 
not nearly so approximate as in the smaller brains and espe- 
23 In the carp, for instance; see Sheldon, R. E. Jour. Comp. Neur., vol. 22 
1912, p. 257, fig. 1 and p. 265, fig. 23. 
