NATURAL THEOLOGY. 



85 



B I perceive it. As they have to make all their 

 motions with their bodies, if their backs were not as 

 jointed and flexible as possible, they would not be 

 able to move ; at least, not with any facility. 



T. Do you see any natural cause why the want 

 of feet should have given them an unusual number of 

 bones in their backs ? 



B. 1 see no cause but design. 



A. The vertebrae of the fah differs from that of 

 the serpent in there being a cavity at each end. Ev- 

 ery joint resembles two cups united together by their 

 edges, so as to leave a hollow inclosed space. This 

 space is filled with a gristly substance less solid than 

 bone. One design may be to diminish the weight of 

 the spine, and render the fish thereby more buoyant 

 in the water. 



The neck joints of the bird are remarkable. It is a 

 structure by which the animal is assisted in smoothing 

 and adjusting its feathers, turning its head backward 

 under the wing, and thrusting out or drawing in its 

 beak with rapidity in collecting its food. In the first 

 place, the vertebrae are not united by flat surfaces, as 

 in quadrupeds. They are rounded at the point of 

 contact, so as to roll upon one another with more ease, 

 and be capable of more flexion. Secondly, the upper 

 joints of the neck can only bend forward, and the un- 

 der ones admit only of a backward motion. The con- 

 sequence is, there are two curvatures in opposite di- 

 rections, like the letter S, so that by spreading or con- 

 tracting them at the same time the neck is lengthened 



H 



