209 



hardly do. Beside, they would want means of breed- 

 ing, having no way to lay their eggs, to sit, hatch, or 

 brood their young. 



Before we conclude this head, it may be observed, 

 that all the parts of birds are fitted for the use of fly- 

 ing. First, as the muscles of the wings are peculiarly 

 strong, so the under side of them is made concave, and 

 the upper convex, that they may be the more easily 

 lifted up, and the more strongly strike the air. Then 

 the trunk of their body somewhat resembles the hull of 

 a ship; the head the prow, which is generally small, 

 that it may the more readily cut the air, and make way 

 for the body. Add to this, that the bodies of birds 

 are small in comparison of beasts, that they may be 

 more easily supported by the air : and they are not 

 only small, but of a broad figure, that they may bo 

 buoyed up the better. They are also hollow and light, 

 yea, their very fcones are light. For even those of 

 the legs and wings have ample cavities : by this means 

 also they become rigid and stiff, it being demonstrable 

 that a hollow body is more stiff and inflexible than a 

 solid one of equal substance. The shafts also of the 

 feathers are either empty or filled with a light and 

 spungy matter; and their webs consist of two rows of 

 contiguous filaments furnished all along with hooks on 

 each side, whereby catching hold of one another they 

 stick fast together. 



As to their tails, although it is true as was observed, 

 that all birds whose tails are pointed and end in aright 

 line, turn themselves by their wings and not their tails, 

 yet in those that have forked tails it is otherwise. Thus 

 it is manifest to sight, that the forked-tailed Kite, by 

 turning her train sideways, raising one horn, and de- 

 pressing the other, turns her whole body. And 

 doubtless the tail has the same use in swallows, who 

 have all forked tails, and make more sudden turns ia 

 the air than any other bird. 



