592 AVES BIRDS. 



activity which brings down the falcon upon his quarry like a thun- 

 derbolt from the clouds, or sustains the migratory bird through 

 long and perilous journey ings. 



But increase of muscular energy is by no means the only conse- 

 quence resulting from more perfect respiration, and a consequently 

 increased temperature of the blood : the clothing of the body must 

 now be changed for a warmer covering than scales or horny plates; 

 feathers are therefore at once provided as the lightest, warmest blan- 

 ket that could be given : maternal care, which to the cold-blooded 

 Ovipara would have been a useless boon, can now be beneficially ex- 

 ercised ; the eggs, no longer left to chance, are cherished by the vital 

 heat of the parent ; and the callow brood, during the first period of 

 their lives, are dependent for support upon the watchful attentions 

 of the beings from whom they derived their existence. 



(658.) The skeleton of a vertebrate animal formed for flight must 

 obviously be constructed upon mechanical principles widely different 

 from any that have yet come under our notice. The utmost lightness 

 is indispensable ; but still, in a frame-work which has to sustain the 

 action of muscles so vigorous, strength and firmness are equally es- 

 sential : it is in combining these two opposite qualities that the 

 human mechanician displays the highest efforts of ingenuity, and by 

 the scientific disposition of his materials exhibits the extent of 

 his resources and the accuracy of his knowledge ; but let the best 

 informed and most ingenious mechanic carefully and rigidly investi- 

 gate the skeleton of a bird, and we doubt not that in it he will find 

 all his art surpassed, and derive not a little instruction from the 

 survey. 



In the spinal column of a bird we find three principal regions, 

 each of which will merit distinct notice. 



The anterior or cervical region is exceedingly variable in its pro- 

 portionate length, and forms the only flexible portion of the spine : 

 it performs, indeed, the office of an arm, at the extremity of which 

 the beak, the chief instrument of prehension, is situated. The 

 number of vertebrae entering into the composition of this part of the 

 spinal column is very variable : in the Swan there are as many as 

 twenty-three ; in the Crane, nineteen ; while in the little Sparrow 

 nine only are met with : their bodies are joined together by articu- 

 lating facets inclosed in synovial capsules, and not by the interposi- 

 tion of intervertebral substance ; an interarticular cartilage, however, 

 is generally met with, by which the movements of the chain are 

 facilitated. The spinous and transverse processes are short ; while 



