PISCES. 



H E general description both of the external and 

 internal parts of Fishes, considered as a distinct 

 tribe of animals, cannot be better detailed than in 

 the works of the ingenious Dr. Monro, who observes 

 that these animals have neither anterior nor posterior 

 extremities, as quadrupeds and birds, their pro- 

 gression being performed in a different method. 

 For this purpose they are provided with machines, 

 properly consisting of a great number of elastic 

 beams, connected to one another by firm mem- 

 branes, and with a tail of similar texture. Their 

 spine is moveable towards the posterior part, and 

 the strongest muscles of their body are inserted 

 there. Their tails are so framed as to contract to a 

 narrow space when drawn together to either side, 

 and to expand again when drawn to a strait line 

 with their, bodies; so that, by the assistance of the 

 broad tail and the fins on the sides, the animals 

 make their progression in the water in much the 

 same way as a boat with oars at its sides, and a 

 rudder at its stern : the perpendicular fins situated 

 v. iv. P. i. 1 



