. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. THE HEART AND ITS VESSELS. 279 In correspondence with the different function which each portion has to perform, the walls of the atrium are thin, while those of the ventricle are much stronger, its muscles giving rise in the interior to a network and also usually series of large trabeculas; this holds good throughout the Vertebrata (Fig. 222, C, Between the ventricle and atrium, at the margins of the atrio- ventricular aperture, membranous valves are present; of these there are usually two,
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. THE HEART AND ITS VESSELS. 279 In correspondence with the different function which each portion has to perform, the walls of the atrium are thin, while those of the ventricle are much stronger, its muscles giving rise in the interior to a network and also usually series of large trabeculas; this holds good throughout the Vertebrata (Fig. 222, C, Between the ventricle and atrium, at the margins of the atrio- ventricular aperture, membranous valves are present; of these there are usually two, but this number may be increased to as many as six (Fig. 222, C, a, a). Numerous valves, arranged in rows, are present in the muscular fruncus or con us arteries us (Fig. 222, C, Ca, 5) ; these are most numerous in Elasmobranchs and Ganoids. There is a tendency however for the posterior ones, or those which lie towards the ventricle, gradually to undergo reduc- tion. The most anterior row always persists, and corresponds to the single row of valves between the ventricle and bulbus in Teleostei. Together with the reduction of these valves, the conus arteriosus of Teleosteans also becomes reduced, so that the non- contractile bulbus arteriosus usually lies close against the ventricle (Fig. 222, B, Ba). e .Al AjC, *Y. FIG. 223.—DIAGRAM OF THE ARTERIAL SYSTEM OF FISHES. H, heart; c, c1, anterior and posterior cardinal veins ; a, branchial arteries ; H, capillaries of the branchial vessels ; b, branchial veins ; ce, circulus cephalicns ; ca, carotids ; EA, root of the aorta ; A, dorsal aorta ; E, artery to viscera (cffiliaco-mesenteric) ; N, renal arteries. The heart of Fishes contains venous blood only, which it forces through the branchial arteries (Fig. 223, «•) into the capillaries. 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 r
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