. The chordates. Chordata. 71 Basic Struct lire of Vertebrates. Fig. 74. Relations and modifications of the post- and subcardinal, abdominal, and postcaval veins in successive developmental stages of an amphibian. (A) The veins (il) from the hindlimb return directly to the heart by the lateral abdominal veins (la), while the blood from the tail (c) passes by way of the subcardinals (sc) through the mesonephroi to the postcardinals (pc). (B) The lateral abdominals have united in front to form the anterior abdominal vein (aa); the iliacs have sent a branch to the postcardinals, which have grown
. The chordates. Chordata. 71 Basic Struct lire of Vertebrates. Fig. 74. Relations and modifications of the post- and subcardinal, abdominal, and postcaval veins in successive developmental stages of an amphibian. (A) The veins (il) from the hindlimb return directly to the heart by the lateral abdominal veins (la), while the blood from the tail (c) passes by way of the subcardinals (sc) through the mesonephroi to the postcardinals (pc). (B) The lateral abdominals have united in front to form the anterior abdominal vein (aa); the iliacs have sent a branch to the postcardinals, which have grown back to join the caudal, while the subcardinals have lost their connection with the caudal and have acquired one with the postcava (p), a backward growth from the sinus venosus. (C) The post- cardinals have been interrupted, the posterior half of each now forming an advehent renal vein (av) while the subcardinals, as in B, form the revehent veins (r). (cd) Duct of Cuvier (precava); (h) hepatic vein; (J) jugular vein. (Courtesy, Kingsley: "Com- parative Anatomy of Vertebrates," Philadelphia, The Blakiston Company.) Hepatic-Portal System. A highly unique feature of the arrange- ment of the veins in a vertebrate exists between the digestive tube and the liver. In general, the blood, in the course of its round trip from heart to tissues and back to heart, passes through only one system of capillaries. But the blood which is delivered by arteries to the walls of the coelomic portion of the digestive tube, having passed into capillaries in the tissues of the tube, is drained away by veins which convey it directly into the liver and distribute it into capillaries throughout the entire mass of the liver (Fig. 64). From these hepatic capillaries the blood is re-collected by the hepatic veins, which then take it directly to the heart. The blood, therefore, in its circuit from heart to heart, has passed through two systems of capillaries. This peculiar set of veins interposed be
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