. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 280 COMPARATIVE ANATOMY. of the gills (72), where it becomes oxygenated, to pass thence into the branchial veins (Fig. 223, 1). The manner in which the aortic roots become formed from the latter has already been described. Dipnoi. — In the Dipnoi, as in Fishes proper, the heart lies far forwards, near the head. In correspondence with the double mode of respiration, by lungs as well as by gills, it reaches a stage of development mid-way between that seen in Fishes and in Amphi- bians. The atrium
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 280 COMPARATIVE ANATOMY. of the gills (72), where it becomes oxygenated, to pass thence into the branchial veins (Fig. 223, 1). The manner in which the aortic roots become formed from the latter has already been described. Dipnoi. — In the Dipnoi, as in Fishes proper, the heart lies far forwards, near the head. In correspondence with the double mode of respiration, by lungs as well as by gills, it reaches a stage of development mid-way between that seen in Fishes and in Amphi- bians. The atrium becomes divided into two chambers by a septum, as does also the ventricle to some extent. The conus arteriosus is. FIG. 221.—DIAGRAM OF THE AND BRANCHIAL VESSELS OF CERATODUS. (.Mainly after J. E. V. Boas.) V, ventricle ; A, A1, atria ; Co, conns arteriosns ; Ca and Cp, anterior and posterior cardinal veins ; DC, duetus Cuvicri ; /toIV, branchial arteries ; 1 to 4, branchial veins ; Ca, carotid ; Ap, pulmonary artery ; RE, capillaries of lung ; J'p, pul- monary vein ; RA, roots of the aorta, beginning at t ; Ao, dorsal aorta. 1 \vistrd spirally on itself (Fig. 224, Cu) : in Ceratodus it is pro- vided with c'k'ht transverse rows of valves, and begins to be divided O O into two chambers. In Protopterus this division is complete, so that two currents of blood, an arterial and a venous, pass out from the heart side by side (Fig. 22o, a,I}. (The former comes from the pulmonary vein, from which it passes into the left atrium, thence into the left ventricle, and so to the two anterior. 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, New York, Macmillan
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