370 
KAMAKICHI KISHINOUYE: 
does not imite with the Cuvierian duct directly. In this genus most of the 
segmental veins running along the haemal spines in the precaudal region and 
also in the anterior part of the caudal region are divided into many venules 
near the vertebral column, so that their blood does not return directly to the 
heart, but seems to be collected to venules above the vertebral column and in 
the dark red portion of the lateral muscle. This is very remarkable. The 
segmental veins in the caudal region unite to a slender caudal vein. 
In Neothunnns the posterior cardinal vein is very conspicuous, and gives 
off a peculiar plexus in the haemal canal, and at last joins the right Cuvierian 
duct. The cutaneous veins are united by an anterier transverse commissure as 
in Paratlmnnus, or sometimes each of them pour directly into the Cuvierian 
duct of the respective side as in Thunnus. A short slender renal vein runs 
under the posterial cardinal vein and is united to it. 
In the Katsuwonidae the vertebral venous system consists of the posterior 
cardinal vein, jugular veins, Cuvierian ducts, lateral veins, cutaneous veins, 
segmental veins, and subspinal plexus. The posterior cardinal vein is con¬ 
nected with a remarkably well developed plexus of venules in the haemal 
canal and joins the right Cuvierian duct as in the genus Neothunnus. The 
cutaneous veins do not join the Cuvierian duct directly, nor are they united 
by a transverse vessel in the thoracic region to the posterior cardinal vein, 
but are divided to renal portals. Thus these cutaneous veins differ from the 
similar veins of the Thunnidae. Moreover the lower cutaneous vein of this 
family is not homologous to the lower branch of the cutaneous vein of the 
Thunnidae. The epaxial and hypaxial veins originate in different myotomes 
and they do not form a loop at the caudal region, nor are they connected by 
a transverse commissure. In Katsuivonus the epaxial and hypaxial cutaneous 
veins are nearly equal in size and length, and though they are not straight 
they are nearly equally distant from the lateral median line of the body. 
These veins run anteriorly and to a deeper part of the body, passing through 
the myotome of the fifth vertebra. The epaxial vein passes below the first rib, 
while the lower passes above it. These two veins receive blood respectively 
from the sheets of vascular plexus on the dorsal and ventral sides of the dark 
red portion of the lateral muscle. In the other genera, Eidhynnus and Auxis, 
the epaxial cutaneous vein is very tliick and runs close and parallel to the 
