. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. CIRCULATION. 649 Fig. Cuttle-fah. the gills has a dilated contractile portion (£>*), which dilatations may be considered as bran- chial hearts, so that there are three separate contractile portions of the circulatory system. In the Gasteropoda and Pteropoda, there is only one heart. This organ is strong and mus- cular, provided with valves, and consisting of an auricular and a ventricular cavity (Jigs. 321 and 322, h, H). In the Testaceous Acephala, the heart is nearly of the same structure as in the orders just
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. CIRCULATION. 649 Fig. Cuttle-fah. the gills has a dilated contractile portion (£>*), which dilatations may be considered as bran- chial hearts, so that there are three separate contractile portions of the circulatory system. In the Gasteropoda and Pteropoda, there is only one heart. This organ is strong and mus- cular, provided with valves, and consisting of an auricular and a ventricular cavity (Jigs. 321 and 322, h, H). In the Testaceous Acephala, the heart is nearly of the same structure as in the orders just mentioned, but less fully deve- loped. In most of them, as also in the Gas- teropodous Mollusca, the rectum passes through the ventricle. The auricle is occasionally double. The Brachiopoda have two aortic hearts, but of a very simple structure, not being divided into auricular and ventricular portions. The naked Acephala, such as the Ascidise, have the simplest heart of all the Mollusca, consisting of a thin membranous ventricle apparently without valves. In all these animals, the course of the blood is generally considered to be the following: Arterial blood only passes through the systemic or aortic heart (or hearts where this organ is double), and is carried to the system by the branches of the systemic arteries (A, «). The VOL. I. altered blood, returning in the veins of the system, is collected into one or more trunks ( F), and carried in the subdivided branches of these (fig. 321, jig. 322, JB) to the re- Fig. 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 Todd, Robert Bentley, 1809-1860. London, Sherwood, Gilbert, and Piper
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