86 SPINE. 



or shortened much more expeditiously. The elegant 

 form of the swan's neck is owing to this construction. 

 But there is more to be noticed. The vertebrae of 

 the back are as remarkable for the rigidity of the joints, 

 as xnose of the neck for their uncommon flexibility. 

 The bird wants a solid support in the back, to sustain 

 the motions of the wings in flying. Had this portion of 

 the spine been as flexible as in other animals, the body 

 would have been liable to be bent or twisted round. 

 The more unwieldly birds which do not fly, are said 

 to be without this construction. 



B. This is the more remarkable, because it seems 

 to be the very reverse of a natural effect. The natural 

 tendency of the exercise of the wings, I should sup- 

 pose, would be to bend the joints of the back and not 

 to stiffen them. 



A. In general the length of the neck is such, that, 

 added to the head, the length of both is equal to the 

 height of the animals' shoulders from the ground. In 

 some fowls it greatly exceeds this proportion. This 

 is necessary to enable them to seek their food below 

 the surface of the water in which they swim. The 

 same proportion is equally remarkable in quadrupeds ; 

 otherwise they could not easily reach the herbs on 

 which they feed, or the water they drink. Among all 

 those in which this rule is observed, the size of the 

 head is less in proportion as the length of the neck is 

 greater. But for this circumstance, the animal would 

 be put to great exertion in raising up his head. This 

 rule, however, is not observed with regard to animals 



