NATURAL THEOLOGY. 243 



from the stroke slantwise. The turning of the 

 oar in rowing, whilst the rower advances his hand 

 for a new stroke, is a similar operation to that of 

 the feather, and takes its name from the resem- 

 blance. I believe that this faculty is not found in 

 the great feathers of the tail. This is the place also 

 for observing that the pinions are so set upon the 

 body as to bring down the wings not vertically, 

 but in a direction obliquely tending towards the 

 tail; — which motion, by virtue of the common 

 resolution of forces, does two things at the same 

 time — supports the body in the air, and carries it 

 forward. The steerage of a bird in its flight is 

 effected partly by the wings, but in a principal 

 degree by the tail. And herein we meet with a 

 circumstance not a little remarkable. Birds with 

 long legs liave short tails ; and in their flight place 

 their legs close to their bodies, at the same time 

 stretching them out backw ards, as far as they can. 

 In this position the legs extend beyond the rump, 

 and become the rudder ; supplying that steerage 

 which the tail could not. 



From the wings of birds, the transition is easy 

 to the fins of fish.^^ They are both, to their re- 



^ This subject is necessarily treated at length in the Bridge- 

 water Treatise of the Hand. We have had occasion to state, that 

 in the higher division of animated nature, the vertebrata, one plan or 

 system of bones can be traced through every variety from man to 

 fishes ; and this is more especially shown by the comparison of the 

 arm with the anterior extremity of quadrupeds and the wing of 

 birds, and even with the pectoral fin of the fish. The number of 

 the bones, and the form and the application of the muscles to them 



