. Comparative anatomy. Anatomy, Comparative. 354 COMPARATIVE ANATOMY vein of Elasmobranchs divides anteriorly into the paired renal portal veins which break up in capillaries within the mesonephroi. The heart resembles that of cyclostomes. The branches of the dorsal aorta are subclavians, intersegmentals, celiac, anterior and posterior mesenteries, spermatics and ovarians, and renals. (Fig. 294, B) Dipnoi. In the dipnoi with the emergence of lungs some advances towards the mammalian circulation are seen. In the heart of lung fishes both atrium and sinus venosus become partly divided by incompl
. Comparative anatomy. Anatomy, Comparative. 354 COMPARATIVE ANATOMY vein of Elasmobranchs divides anteriorly into the paired renal portal veins which break up in capillaries within the mesonephroi. The heart resembles that of cyclostomes. The branches of the dorsal aorta are subclavians, intersegmentals, celiac, anterior and posterior mesenteries, spermatics and ovarians, and renals. (Fig. 294, B) Dipnoi. In the dipnoi with the emergence of lungs some advances towards the mammalian circulation are seen. In the heart of lung fishes both atrium and sinus venosus become partly divided by incomplete longitudinal septa. Impure blood from the veins enters the right atrium while aerated blood from the lungs flows into the left atrium. Atrio- ventricular valves are lacking but the conus contains a series of Fig. 296.—Diagram of vertebrate circulation based on a urodele. Arteries cross- lined; veins black except the pulmonary vein, white, av, abdominal vein; c, celiac artery; ca, cv, caudal artery and vein; d, dorsal aorta; ec, external carotid; g, gonad; h, hepatic vein; ha, hepatic artery; hy, hypogastric artery; ic, internal carotid; il, iliac artery and vein; j, jugular; Iv, liver; m, mv, mesenteric artery and vein; pa, pulmonary artery; pcd, postcardinal; pcv, postcava; pv, hepatic portal vein; r, rectal artery; ra, renal advehent (portal) vein; sc, subclavian artery and vein. (From Kingsley's "Comparative Anatomy of ;) Immediately in front of the conus the truncus divides into four pairs of aortic arches, the third to the sixth of the original series. In the dipnoi pulmonary arteries make their first appearance in the vertebrate series as posterior branches of the last pair of aortic arches. As another novelty in fishes, the right postcardinal vein degenerates and a new vein, the postcava, drains most of the posterior part of the body. The caudal vein in this group bifurcates into the left postcardinal and the postcaval veins. The ilia
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Keywords: ., bookcentury1900, bookpublisherphi, booksubjectanatomycomparative
