46 LECTURE VIII. 



jointed rays towards the back-part. By the 

 various flexure therefore of these organs, the 

 movements of Fishes are conducted ; the perpen- 

 dicular fins, situated on the back or upper part of 

 the animal, keeping the body in equilibrio, while 

 the tail, which is also perpendicular in its direc- 

 tion, and capable of various flexures and contrac- 

 tions, operates as a rudder at the stern of a vessel, 

 and the side or breast-fins as oars. 



With respect to the internal parts of Fishes, 

 it is observed that the throat is short; the stomach 

 large, and the intestines far shorter than in qua- 

 drupeds and birds: the liver very large, and 

 usually placed on the left side. In the majority of 

 Fishes occurs under various shapes, a highly cu- 

 rious and important organ called the air-bladder 

 or swimming-bladder : it generally lies close be- 

 neath the back-bone, and is provided with a very 

 strong muscular coat, which gives it the power of 

 contracting at the pleasure of the Fish, so as to 

 condense the contained gas or elastic air with 

 which it is filled, and thus enable the animal to 

 descend to any depth, and again to ascend by 

 being restored to its largest size. In some Fishes 

 it is found to communicate with the throat j in 



