. The Cambridge natural history. Zoology. 328 FISHES . two cavities are connected by a single pericardio-peritoneal canal, or by two such canals; and in Ghimaera, and in the Sturgeon {Aci]penser) and Polyodon, by a single canal. The heart consists of at least three chambers, a sinus venosus which receives the venous blood from the body, an auricle and a ventricle, to which is added a conus arteriosus in the Elasmo- branchs, certain Teleostomi (Crossopterygii, Chondrostei, and Holostei), and in the Dipnoi. Through these cardiac chambers the blood is forced ui the order mentioned. In the Di
. The Cambridge natural history. Zoology. 328 FISHES . two cavities are connected by a single pericardio-peritoneal canal, or by two such canals; and in Ghimaera, and in the Sturgeon {Aci]penser) and Polyodon, by a single canal. The heart consists of at least three chambers, a sinus venosus which receives the venous blood from the body, an auricle and a ventricle, to which is added a conus arteriosus in the Elasmo- branchs, certain Teleostomi (Crossopterygii, Chondrostei, and Holostei), and in the Dipnoi. Through these cardiac chambers the blood is forced ui the order mentioned. In the Dipnoi the auricle is subdivided by a more or less complete inter- auricular septum into a right and left auricle,^ the former receiving the venous blood from the sinus venosus, and the latter the aerated blood from the lung-like air- bladder. The sinus venosus and the auricle have very thin walls ; the ventri- cular walls, on the con- trary, are very thick and m great measure are composed of a sponge-like network of mus- cular bundles which generally encroaches considerably on the ven- tricular cavity. Membranous valves, the sinu-auricular, and the auriculo-ventricular valves, are developed at the junctions of the sinus venosus with the auricle, and the auricle with the ventricle respectively. The conus arteriosus is muscular and contractile, and is interposed between the ventricle and the root of the ventral aorta. Internally, the conus is provided with several transverse rows of pocket-shaped or semilunar valves. In Teleosts the conus is non-muscular and vestigial, and has but a single row of valves, corresponding to the most anterior of the multiple rows of valves in the Elasmobranchs. In these 1 There is an incomplete auricular septum in the Holooephali ( Ghimaera monstrosa), see Bay Lankester, Trans. Zool. Soc. x. 1879, p. Fig. 193.—Diagram of the structure of the heart in different Pishes. A, In an Elasmobranch ; B, in Amia; and C, in a Teleost. a. Auricle;
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
