652 PISCES. 



between two folds of the intestine (fig. 317, w), and evidently, in position, 

 presenting no precise relations with the stomach. It receives a large 

 Supply of arterial blood, which becomes converted into venous as it 

 circulates through this organ, and in that state is transmitted to the 

 liver through the portal system of veins. 



(1785.) Another important addition to the animal economy, peculiar 

 to the Vertebrate division of animals, is the lymphatic or absorben 

 system of vessels, which in Fishes are abundantly distributed through the 

 body, and ramify like a rich network over the walls of the intestine. 

 These pour the materials absorbed from the body, and the products of 

 digestion, into the principal venous trunks, to be mixed up with the 

 circulating blood *. 



(1786.) The circulation of the blood in Fishes is carried on by the 

 assistance of a heart composed of two cavities only, which receives the 

 vitiated blood after it has circulated through the system, and propels it 

 through the branchiae, where it is exposed to the influence of the oxygen 

 contained in the surrounding medium. After being thus purified, the 

 blood is collected from the respiratory organs by the radicles of the 

 branchial veins ; and these latter vessels, by their union, form the aorta. 



A Fig. 318. B 



A. Heart of Lophius piscaforiua. B. Ordinary structure of a Fish's heart. In both drawings, 

 a, represents the vena cava ; 6, the auricle ; c, the ventricle ; d, the bulbus arteriosus ; and 

 0, the valvular apparatus guarding its commencement. 



There is, therefore, no systemic heart in Fishes, the aorta itself serving 

 to propel the slow-moving blood in its course through the arterial 

 system. 



* For a detailed account of the lymphatic system of Fishes, the reader is referred 

 to the following authors : Monro, ' Anat. and Physiol. of Fishes,' fol. ; Hewson, Phil. 

 Trans. 1769; Fohmann, 'Histoirc ge"nerale des Lymphatiques des Vertebras,' Hei- 

 delberg and Leipzig, fol. 1827. 



