. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. A FIG. 306.—DIAGRAM SHOWING THE COURSE OF THE BLOOD THROUGH THE HEART ix UrodfJa (A) AND Anura (B). A, right atrium ; A1, left atrium ; ir, fi; pulmonary veins; tr, conus arteriosus, divided in Anura (B) into two portions, tr, tr1 : through tr -venous blood passes into the pulmonary arteries, Aj>}, Aj>1, while through tr1 mixed blood goes to the carotids, ci—<'e, and to the roots of the aorta, Ft A ; V, ventricle ; 11, v, pre- and postcavals (only one precaval is indicated). are always two sinu-atrial valves and
. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. A FIG. 306.—DIAGRAM SHOWING THE COURSE OF THE BLOOD THROUGH THE HEART ix UrodfJa (A) AND Anura (B). A, right atrium ; A1, left atrium ; ir, fi; pulmonary veins; tr, conus arteriosus, divided in Anura (B) into two portions, tr, tr1 : through tr -venous blood passes into the pulmonary arteries, Aj>}, Aj>1, while through tr1 mixed blood goes to the carotids, ci—<'e, and to the roots of the aorta, Ft A ; V, ventricle ; 11, v, pre- and postcavals (only one precaval is indicated). are always two sinu-atrial valves and two atrio-ventricular valves, the latter of which are connected with the walls of the ventricle by cords. The two pulmonary veins unite before opening obliquely, as in all the higher Vertebrates, into the left atrium, at which point there are no special valves: the two precavals and the postcaval open independently into the sinus venosus. 1 The largest of these, as well as the fibrous cushion described above, take a greater part in separating the two auricles than does the septum proper. - In the lungless Urodeles (cf. p. 378) the septum atriorum and pulmonary vein are wanting, though the pulmonary artery can still be recognised. D D*. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wiedersheim, Robert, 1848-1923; Parker, W. N. (William Newton), d. 1923. London, Macmillan and co. , limited
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