COMPARATIVE STUDY OF SCOMBROID FISHES. 
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ventral. Those numerous arterioles nourishing the dark red portion of the 
lateral muscle run axially. In Eutliynnus and Auxis there are two pairs of cutaneous 
arteries originating from two different points. The anterior pair is smaller, 
homologous to the hypaxial limb of the cutaneous artery of Katsuivonus, and 
is given off from the body segment of the sixth vertebra. The artery takes a 
more or less forward direction, passes through the kidney and then turns 
backwards. The artery has no relation with the dark red muscle. The 
posterior pair is very thick, nearly as thick as the dorsal aorta or a little 
thicker than it, probably homologous to the whole cutaneous artery of the 
Thunnidae. The posterior pair of cutaneous arteries takes an obliquely upward 
and backward direction, and makes its appearance at the surface of the body, 
between the intermuscular bones of the fourth and fifth vertebrae. The artery 
runs a little above the lateral median line, and seems to vanish in the caudal 
part. The cutaneous artery sends off segmental branches to the surface of the 
body, both dorsal and ventralwards, and axially very numerous arterioles to 
the dark red portion of the lateral muscle. These arterioles are arranged in 
two diverging sheets to invest the dark red portion of the lateral muscle. In 
a rare abnormal case, I found the posterior cutaneous artery joined to the anterior 
cutaneous artery, but in such cases the abnormality is found in one side of the 
body only. 
In the Plecostei subspinal vascular plexus or the kurochiai, the vascular 
plexus in the haemal canal, deserve attention. In Neothunnus vertical arterioles 
originate as short parallel numerous vessels from the dorsal aorta in the same 
way as the accompanying venules originate from the cardinal vein and these 
together make a black red rod as tliick as a thumb. These numerous arterioles 
unite again to two pairs of segmental arteries in each body-segment, one along 
the intermuscular bone, the other along the neural spine. In the Katsuwonidae 
the subspinal vascular plexus does not He just beneath the vertebral column 
but is more or less separated from the latter. In Eutliynnus and Auxis 
(fig. 2) the dorsal aorta is so remarkably separated from the vertebral column 
that the kurochiai is bent like a bow. In Auxis the arterioles are few in 
number and the subspinal vascular plexus is much degenerated. The oblique 
segmental arteries from the dorsal aorta nourish the dark red portion of the 
lateral muscle from the axial side. 
