372 
KAMAKICHI KISHINOUYE : 
hepatic veins ai‘e divided very finely and run quite near tlie external surface 
of the liver. In Parathunnus venules of the hepatic veins on the external 
surface of the liver are rather short and sparce, while in Neothunnus venules 
of the hepatic veins are few, large and are not found at the external surface 
of the liver. In immature forms of our common tunny venules on the surface 
of the liver are short, remarkably shorter than in the adult. In the Katsuwonidae 
neither the plexus nor the parallel venules among the viscera nor those on 
the external surface of the liver are found. In Auxis, however, black dendritic 
figures of the hepatic veins are noteworthy on the external surface of the liver. 
In Euthynnus and Auxis the right lobe of the liver is elongated, and hepatic 
portal veins from the pyloric coeca run in many transverse canals to the lobe. 
Heart. The heart lies just before the pericardo-peritoneal septum, in a 
more or less conical space, enclosed and protected by the lower pliaryngeals, 
clavicles, and pelvic girdle. The organ consists of a sinus venosus, amide, 
ventricle, and bulbus arteriosus. The sinus venesus is thin-walled and spacious,, 
formed by the union of the Cuvierian ducts below the oesophagus. The sinous 
communicates with the auricle by a round opening. The auricle is a more or 
less flattened sac with a triangular outline, covering the dorsal anterior face 
of the ventricle. The inner side of its wall is reticulated with muscle bundles. 
The ventricle is firm, thick walled, more or less tetrahedral in shape, with an 
i 
anterior vertex, ventral edge, and posterior base. In the anterior dorsal face 
the ventricle is connected with the preceding chambers. Thus here the course 
of blood-circulation is changed. The posterior face or the base is flat or rather 
a little concave. The bulbus arteriosus is a laterally compressed sac, ovoidal 
in form, with a well developed muscular wall. The sinu-ventricular orifice is 
elliptical with two large pocket-shaped valves, while the auriculi-ventricular 
orifice is roundish, guarded with four hood-like valves. The size of the heart 
is remarkably large in the Plecostei as it propels more blood than in the 
Teleostei. The form of the heart is different in the Plecostei, the base of the 
ventricle is nearly vertical in the order, wliile in the Scombridae and Cybiidae 
it is oblique. 
Arterial system. The bulbus arteriosus gradually passes to the short 
ventral aorta which gives off four pairs of afferent branchial arteries. The 
aeriated blood in the gill-arches is mostly carried dorsalwards to the efferent 
