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KAMAKICHI KISHINOUYE : 
ventral side of tlie skull, in the otic region. 
Fig. K. Dorsal view of the brain. 
1, Scomber japonicus ; 2, Cybium niphonium ; 3, Thunnus orientalis ; 4, Thunnus germo ; 
5, Katsuwonus pelamis ; 6, Auxis maru (dorsal &, lateral) ; 7, Euthynnus yaito. 
In the Plecostei the brain is tliicker than that of the Teleostei, and the 
cerebellum covers the whole length of the brain, behind the prosencephalon. 
The external surface of the prosencephalon and cerebellum is not flat. The 
former is divided into four longitudinal lobes, and the latter into several areas 
by the median longitudinal and transverse grooves. 
Ganglia of the sympathetic nerve are found in the haemal canal, one in 
each body-segment, and when the canal is filled with the vascular plexus, they 
are embedded in it. 
The otolith is rather thick and the parts on each side of the median groove 
are nearly equal in the Scombridae. In the Cybiidae one side is longer than 
the other, and in Gymnosardci the longer side is very much elongated and is 
nearly twice the length of the other. In the Thunnidae the otolith is straight, 
and one side is much longer than the other. In the Katsuwonidae the otolith 
is very slender and the parts on both sides of the groove are equally well 
developed, the hind end being more or less swollen. 
