46 
LECTURE. VIIL 
jointed rays towards the back-part..- By tlie 
various flexure therefore of these organs, the 
movements of Fishes are conducted 5 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, whicli 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 ^ in 
