36 THE BONES. 



rially from those of four-footed animals, being composed 

 of a thin, firm, and partly elastic substance, formed in 

 layers, apparently fastened together, and almost always 

 hollow; the cavities never containing marrow, but air, 

 and communicating with the lungs by considerable open- 

 ings ; whereby they are rendered buoyant and light to a 

 much greater degree than is generally supposed. Thus 

 a portion of the leg of a Goose, about two inches in 

 length, weighed about forty grains, while a piece of the- 

 leg of a rabbit (the marrow having been extracted, and 

 both being perfectly dry, and as nearly as possible of 

 the same thickness and length,) weighed seventy-five 

 grains, or nearly twice the weight of the similarly-sized 

 bone of the Goose ; and yet so firm and strong was this 

 latter, that, although in diameter it was less than one- 

 eighth of an inch, and the solid tubular part not more 

 than one-hundredth part of an inch in thickness, it 

 could not be broken asunder by the hand. 



It is upon this principle mechanics and engineers act 

 in constructing strong supports, knowing that if any 

 quantity of material is to be fabricated into a rod of a 

 certain length, the rod will be strong in proportion to 

 its thickness ; and that if the figure remains the same, 

 that thickness can only be increased by making it hollow. 

 Therefore hollow rods or tubes of the same length and 

 quantity of matter have more strength than solid ones 

 of less diameter. This is but one out of the hundreds 

 of instances, in which the wisdom of man has been per- 

 fected by studying the mode by which the great Creator 

 accomplishes His purposes. 



It is evident that a creature thus furnished with bones 

 so much lighter than those of other animals, must have 

 a prodigious advantage in raising itself in the air. But,. 

 besides this superior lightness of the skeleton, these 

 bones, from their hollow structure, act as pipes sup- 

 plying air in abundance; and thus not only rendering- 

 the bird still lighter, but enabling it to breathe at 

 heights, at which a human being would be gasping far 



