4) BLOOD VESSELS TO THE GASTROINTESTINAL TRACT

The dorsal aorta sends out several unpaired arteries to the abdominal organs: the celiac, anterior mesenteric, and posterior mesenteric arteries.   In higher vertebrates, the hepatic, left gastric, and splenic arteries originate from the celiac.  Lampreys have four arteries including the celiac artery although there is no mesentery ( Hardisty 250).

Shark:

FROG

OPOSSUM

CAT

MONKEY

HEPATIC PORTAL VEIN

     In Amphioxus, there is a large subintestinal vein which transports nutrients from the gut cranially. In Amphioxus, the hepatic portal vein forms a plexus of vessels in the hepatic cecum which rejoin to form the hepatic vein and subsequently the portion of the endostylar artery called the sinus venosus.  (Ruppert, from Harrison, 1997, p. 445-52; Willey 49,54).  The hepatic portal system, which brings blood directly from the GI tract to the liver, has been little modified since the early chordates.  In both lancelets and hagfish, the hepatic portal vein is contractile (Guenther, 154).  This subintestinal vein in the early embryo is formed from the vitelline veins of the yolk (Hardisty).  In vertebrates with a large amount of yolk, (and in mammals, because they evolved from reptilian ancestors with large amounts of yolk), prominent vitelline veins join the subintestinal vein. 

SHARK

GAR

LUNGFISH

SALAMANDER

OPOSSUM

CAT