. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. THE HEART AND ITS VESSELS. 281 branchial arteries (Fig. 225, /, 77). The venous current, on the other hand, passes from the right ventricle into the third and fourth branchial arteries and thence to the corresponding gills, where it becomes purified ; it reaches the aortic arches by means of the branchial veins (///, IV, 3, 4, RA}~^ The pulmonary artery (Ap) arises from the fourth branchial vein, so that the blood is thus. Ao FIG. 225.—DIAGRAM OF THE BRANCHIAL CIRCULATION OF PROTOPTERUS. Co, con
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. THE HEART AND ITS VESSELS. 281 branchial arteries (Fig. 225, /, 77). The venous current, on the other hand, passes from the right ventricle into the third and fourth branchial arteries and thence to the corresponding gills, where it becomes purified ; it reaches the aortic arches by means of the branchial veins (///, IV, 3, 4, RA}~^ The pulmonary artery (Ap) arises from the fourth branchial vein, so that the blood is thus. Ao FIG. 225.—DIAGRAM OF THE BRANCHIAL CIRCULATION OF PROTOPTERUS. Co, conns arteriosus, which consists of two divisions, a and b : through 5 pure arterial blood passes to the two anterior branchial arteries (7 and //) ; through a venous blood passes to the two posterior branchial arteries (/// and IV); 3 and 4 indicate the branchial veins and capillaries of the gills ; Ap, the pulmonary artery, present only on the left side (?) ; RA, arch of the aorta ; Ao, aorta ; Ca, carotid. once more purified before it passes by means of the pulmonary vein into the left ventricle. In Ceratodus the lung is supplied with blood from the cceliac artery, and owing to the fact that the longitudinal valve of the conus is incomplete, the blood passing to the two anterior branchial arteries is of a mixed nature (comp. Fig. 224, /, II}. Amphibia.—With the exception of the Gyninophiona, in which it is situated some distance back, the heart in all Amphi- bians lies far forwards, below the anterior vertebras. As in the Dipnoi, there is a more or less complete septum atriorum (that is, the septum is either entire or fenestrated). There are always two fibrous pocket-like atrio-ventrieular valves, which are con- nected with the walls of the ventricle by cords. The cavity of the ventricle is unpaired, and neither in Urodela nor Anura shows any trace of a septum, so that the blood passing out from it must have a mixed character (Fig. 226). The ventricle is usually of a short
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