. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. CIRCULATION. 647 Fig. FM. through the branches of the aorta (A) in the various parts of the systemic circulation. Dr. Marshall Hall* and J. Mullerf have observed a dilated contractile part of the caudal vein in the tail of the Eel, to which Dr. Hall has applied the name of caudal heart, which may assist in promoting the flow of blood in the caudal branches of the vena cava. The position and anatomical relation of the heart of fishes with the bloodvessels as well as other parts shew that it corresponds to the whole
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. CIRCULATION. 647 Fig. FM. through the branches of the aorta (A) in the various parts of the systemic circulation. Dr. Marshall Hall* and J. Mullerf have observed a dilated contractile part of the caudal vein in the tail of the Eel, to which Dr. Hall has applied the name of caudal heart, which may assist in promoting the flow of blood in the caudal branches of the vena cava. The position and anatomical relation of the heart of fishes with the bloodvessels as well as other parts shew that it corresponds to the whole heart of higher animals, and that the arterial vessel which receives the whole of the fish's blood from the ventricle may strictly be considered as the commencement of an aorta entirely destitute of any pul- monary branches. Although there is no dis- tinct right ventricle to propel the blood to a pulmonary organ, and the whole of the blood issuing from the heart is sent directly to the gills, there is not on this account any suf- ficient reason for considering, as some have done, the heart of the fish as corresponding to * Essay on the Circulation of the Blood, p. 170. Lond. 1831. t Handbuch der Physiol. vol. i. the pulmonary or right cavities of the heart in warm-blooded animals, for we have seen that in some of the reptiles when they have gills, the blood is driven into these organs through the aorta or systemic trunk. The branchial arteries in fishes, as in reptiles, are therefore branches of the great aortic trunk, and the returning vessels on the posterior side of the arches, or branchial veins as they are called, are as much of an arterial nature both in their structure and relations as the anterior vessels or branchial arteries are. When these return- ing vessels unite together on the back to form the descending aorta, it is not necessary there- fore to suppose them to undergo a change from the venous to the arterial structure. So far then as general structure and relat
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