COMPARATIVE ANATOMY. 133 



sage from the mouth to the vent. The longest is in the 

 deer kind. The intestines of a Canadian stag, four feet 

 high, measured ninety-six feet.* The intestine of a sheep, 

 unravelled, measures thirty times the length of the body. 

 The intestines of a wild cat is only three times the length 

 of the body. Universally, where the substance upon v/hich 

 the animal feeds, is of slow concoction, or yields its chyle 

 with more difficulty, there the passage is circuitous and 

 dilatory, that time and space may be allowed for the change 

 and tlie absorption which are necessary. Where the food 

 is soon dissolved, or already half assimilated, an unneces- 

 sary, or perhaps, hurtful detention is avoided, by giving to 

 it a shorter and a readier route. 



V. Id comparing the hones of different animals, we are 

 struck, in the bones of birds, with diproprietij, which could 

 only proceed from the wisdom of an intelligent and design- 

 ing Creator. In the bones of an animal which is to fly, the 

 two qualities required, are strength and lightness. Where- 

 in, therefore, do the bones of birds (I speak of the cylindri- 

 cal bones) differ, in these respects, from the bones of quad- 

 rupeds ? In three properties, first, their cavities are much 

 larger in proportion to the weight of the bone, than in those 

 of quadrupeds ; secondly, these cavities are empty ; thirdly, 

 the shell is of a firmer texture, than is the substance of 

 other bones. It is easy to observe these particulars, even 

 in picking the wing or leg of a chicken. Now, the weight 

 being the same, the diameter, it is evident, will be greater 

 in a hollow bone than in a solid one ; and, with the diame^ 

 ter, as every mathematician can prove, is increased, cceteris 

 paribus, the strength of the cylinder, or its resistance to 

 breaking. In a word ; a bone of the same loeight would 

 not have been so strong in any other form ; and, to have 

 made it heavier, would have incommoded the animal's 

 flight. Yet this form could not be acquired by use, or the 

 bone become hollow and tubular by exercise. What appe- 

 tency could excavate a bone 1 



VI. The lungs also of birds, as compared with the lungs 

 of quadrupeds, contain in them a provision, distinguishingly 

 calculated for this same purpose of levitation ; namely, a 

 communication (not found in other kinds of animals) be- 

 tween the air-vessels of the lungs and the cavities of the 

 body ; so that by the intromission of air from one to the 

 other, at the will, as it should seem, of the animal, its body 



* Mem. of Acad, Paris, 1701, p. 170, 



