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BLOOD VESSELS 2

3)     POSTERIOR LONGITUDINAL VESSELS

     Primitively, a single dorsal aorta and a pair of cardinal veins transport blood along the longitudinal axis of the body.

HAGFISH

SHARK

SHARK

SHARK

GAR

GAR

PERCH

PERCH

PERCH
In sarcopterygian fish, a posterior vena cava formed.  Distinct posterior cardinal veins enter the sinus venosus but they are reduced in size.  In tetrapods, the only adult remnant of the posterior cardinal veins is the azygos vein.

SALAMANDER

SALAMANDER

With the modification of the aortic arches, there were two systemic aortic arches (IV) which fused posterior to the heart to form the dorsal aorta.  This system is retained in amphibians and reptiles.

FROG

FROG

TURTLE

TURTLE