SOME SUGGESTIONS FOB BIRD STUDY. 



109 



Skeleton of Birds. 



Note and verify as far as possible the following 

 points : 



(1) The bones are light, being hollow or of spongy 

 texture. 



(2) Where rigidity 

 is required, parts which 

 are free in other ani- 

 mals have been united 

 in birds. Examples of 

 this are seen in the fol- 

 lowing : 



(a) Backbone, which 

 behind the shoulder 

 is practically rigid 

 throughout. This ob- 

 viously gives leverage 

 to the wing stroke 

 which an ordinary 

 flexible back could not 

 supply. 



(6) Hand portion of 

 the wing, separate fin- 

 gers are not required, 

 rigidity being of more 

 service. The thumb 

 is distinct, and photo- 

 graphs of birds in 

 flight show that some 

 of them make indepen- 

 dent use of the thumb 

 wing. 



(c) Ankle and foot. Eigidity here again in birds is of 

 more value than flexibility. 



(3) Loss of parts. The loss of fingers in the wing has 

 already been referred to. 



Fig. 34. Skeleton of the Pigecn. 



