A FISH BRAIN FROM THE COAL MEASURES 149 
lobes, and a medial ‘tuberculum impar,’ which is formed by a 
fusion of the two facial lobes.1® 
In the absence of information regarding the internal structure 
of the vagal lobes of the Coal Measures fish, it is impossible to 
make safe comparisons with recent fishes. It is not improbable 
that this ‘vagal lobe’ includes the lobus VII and the lobus IX + 
X fused into a single dorso-medial mass, a condition not known 
to occur in any living fish. If this is the correct interpretation, 
this fossil resembles the teleosts in this region more than any 
known ganoid, dipnoan or elasmobranch. The brain of Rhadi- 
nichthys from the Mississippian, unfortunately, does not have 
the vagal lobe preserved. 
_ Between the vagal lobe and the cerebellum in Rhadinichthys 
from the Mississippian are two pairs of eminences which are 
marked ‘tuberculum acusticum’ in figure 4. The same rela- 
tions prevail in the Coal Measures fish, save that the members 
of the posterior pair are fused into a single dorso-medial emi- 
nence (fig. 15). Since we are ignorant of the internal structure 
and connections of these eminences, it is impossible to determine 
their homologies. 
In recent elasmobranchs and ganoids the area acustico-later- 
alis, or tuberculum acusticum, which receives the VIII and lat- 
eral line roots, is represented on each side of the medulla oblon- 
gata by a thickening of the rhomboidal lip which consists of two 
parts. These are very clearly seen in the sturgeon, Acipenser, 
as described by Johnston.17 There is a relatively undifferentiated 
posterior part of this thickening, which is termed by Johnston 
the tuberculum acusticum, and an enlarged anterior lobe im- 
mediately behind the cerebellum, the lobus lineae lateralis (lobus 
trigemini of Goronowitsch). The cerebellum is a thickening of 
the rhomboidal lip of each side immediately in front of the lobus 
lineae lateralis, these structures being functionally very inti- 
mately related. The relations of these parts in Necturus and 
* 
16 See Herrick, Jour. Comp. Neur., vol. 15, 1905, p. 380, fig. 3 and p. 385, fig. 5. 
17 Johnston, J.B. The brain of Acipenser. Zool. Jahrb., Bd. 15, 1901, plate 2, 
figs. 5, 6, 7; also, The nervous system of vertebrates, Philadelphia, 1906, p. 16. 
fig. 3 and pp. 130-141. 
