2 PISCES. 



on the superior part of the body keep them In eqtti- 

 librio, hindering the belly from turning upwards, 

 which it would otherwise easily do ; the air-bag in 

 the abdomen rendering that part specifically lighter 

 than the back: but by the resistance which these 

 fins meet with when inclined to either side, the 

 animals are kept with the back uppermost. A more 

 ample explanation of this particular may be found 

 in Borelli's work de motu animalium. 



Fishes have nothing which can properly be called 

 a neck, since they seek their food in an horizontal 

 direction, and can move their bodies either upwards 

 or downwards, as they have occasion, by the con- 

 traction or dilatation of the air-bag. A long neck, 

 as it would hinder their progression, would be very 

 disadvantageous in the element in which they are 

 .destined to reside. 



The teeth differ in the different tribes, but the 

 generality of Fishes are unprovided with strong teeth, 

 or such as are calculated for breaking and grinding 

 the food, which usually consists of small fishes or 

 other animals that heed no tritu ration in the mouth, 

 but spontaneously dissolve into a liquid chyle; 

 their teeth rather serving to grasp their prey, and 

 hinder it from escaping. For the same purpose the 

 internal cartilaginous basis of the bronchi and the 

 two round bodies situated in the posterior part of 

 the jaws have a great number of tenter-hooks fixed 

 into them, in such a manner as to permit any thing 

 easily to get down, but to be prevented from return- 

 ing ; the superfluous water, which is necessarily re- 

 ceived along with the food, passing between the 



