FISHES. 343 



The spleen varies greatly in its form and position in the 

 animals of this class. In some it is nearly triangular, while 

 in others it approaches to a spherical figure. It is in gene- 

 ral entire ; in some instances, however, it is divided into 

 lobes, which adhere by very slender filaments. In the stur- 

 geon, these lobes are seven in number, while in the angel 

 shark they are limited to two. It is placed in some species 

 on the stomach, or to the first part of the intestines ; in 

 others between the stomach and liver ; and in a great num- 

 ber it is under the air-bag, and above the other bowels. It 

 is always of a darker colour than the liyer. 



While in reptiles the whole blood does not pass through 

 the aerating organs in succession, in the course of circula- 

 tion, it is otherwise with fishes. The heart which they 

 possess is pulmonic, receiving the blood from the veins, 

 and transmitting the whole of it to the aerating organs. It 

 is situate in the fore part of the body, in a cavity between 

 the gills, and a little behind. The pericardium or mem- 

 brane, which lines this cavity, is similar to the covering of 

 the cavity of the abdomen, and, like it, is often spotted 

 or silvery. In the skate, Dr Monro found the bottom 

 of the pericardium lengthened into the shape of a funnel, 

 which divides into two branches. These are tied closely 

 to the lower part of the oesophagus, and open into the ca- 

 vity of the abdomen. Into this cavity there is secreted a 

 saltish liquor. The heart itself is small in proportion to 

 the body of the animal, and varies greatly in figure in the 

 different species. It is quadrilateral in some, and semicir- 

 cular in others. It consists, as we have already mentioned, 

 of a single auricle and a single ventricle, corresponding to 

 the riffht side of the heart of warm-blooded animals. The 

 auricle is in general larger than the ventricle, and of a thin- 

 ner texture in its coats. This last division of the heart has 

 walls of considerable thickness. It sends forth an artery, 



