PISCES FISHES. 517 



(549.) The liver of fishes is proportionately very large, and 

 generally contains abundance of oil. The bile derived from it is 

 received into a gall-bladder (Jig. 227, c), from which a duct of 

 variable length in different species conveys it into the intestine, in 

 the immediate vicinity of the pylorus. 



(550.) It is in these animals that we for the first time find the 

 biliary secretion separated from venous blood; and consequently 

 they are provided with a new arrangement of the blood-vessels of the 

 abdomen, which they possess in common with the other Vertebrata, 

 forming what is termed by anatomists the system of the Vena 

 Porta. The veins derived from the stomach, the intestines, and 

 the spleen, which last viscus now makes its appearance, instead of 

 conveying their contents to the heart, plunge into the substance of 

 the liver, and there again subdivide into capillary tubes ; thus fur- 

 nishing to the liver abundance of venous blood from which the 

 hepatic secretion is elaborated. 



(551.) The Spleen, now for the first time met with in the 

 animal creation, is a highly vascular organ, generally enclosed in 

 the mesentery between two folds of the intestine (Jig. 227, m ; Jig. 

 236, x), 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. 



(552.) Another important addition to the animal economy, pe- 

 culiar to the Vertebrate division of animals, is the lymphatic or ab- 

 sorbent system of vessels, which in fishes are abundantly distributed 

 through the body, and ramify like a rich net- work over the walls of 

 the intestines. 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.* 



(558.) The circulation of the blood in fishes is carried on by 

 the assistance of a heart composed of two cavities only, which re- 

 ceives the vitiated blood after it has circulated through the system, 

 and propels it through the branchise, 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 ves- 



* 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 ; Fohman, Hist. Generate des Lymphatiques des Verteb. ; Heidelberg and 

 Leipzig, fol. 1827. 



