OSTEOLOGY OF BIRDS. 717 



intense, is ready to exert that vigorous activity which brings down the 

 falcon upon his quarry like a thunderbolt from the clouds, or sustains 

 the migratory bird through long and perilous journeyings. 



(2029.) But increase of muscular energy is by no means the only 

 consequence 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 blanket that 

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

 would have been a useless boon, can now be beneficially exercised ; 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. 



(2030.) 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 framework which has to sustain the 

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

 tial : 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 inge- 

 nious mechanic carefully and rigidly investigate 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. 



(2031.) In the spinal column of a bird we find three principal 

 regions, each of which will merit distinct notice. 



(2032.) The anterior or cervical region is exceedingly variable in its 

 proportionate 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 

 vertebras 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 articulating facets enclosed in 

 synovial capsules, and not by the interposition of intervertebral sub- 

 stance ; 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 the oblique processes, united by 

 articulating surfaces, limit the mobility of the neck. 



(2033.) Although this portion of the spine is very properly designated 

 the " cervical region," we are not on that account to imagine that the 

 vertebras composing it are unprovided with ribs : on the contrary, rudi- 

 mentary costal appendages are generally found connected with their 



