364 FLEXIBLE STERNA. 



are also much more omnivorous, and on this, as well 

 as on other accounts, they ought in a perfectly natu- 

 ral system to stand as a separate family, if not as a 

 distinct sub-order. 



Before proceeding to notice the sternal apparatus 

 of the gallinaceous tribe, it may not be improper to 

 remark that the flexibility of the lateral parts of 

 sterna produced by notches of the bone, or cartila- 

 ginous continuations, are intimately connected with 

 the power of walking straight forward upon two legs, 

 in birds which have the use of their wings in flight, 

 and which consequently have furcal or clavicular 

 bones, though the form and strength of these vary 

 with the powers of flight. 



It will be readily understood that the clavicle ties 

 the shoulder-joints together, and the coracoids at the 

 same time keep them both at equal distances from 

 the anterior angles of the sternum, so that the line 

 joining the shoulder-joints is immoveable in position 

 with reference to the sternum, except in so far as the 

 different articulations are loose and admit of play, 

 and the change of position produced in this way is 

 very limited. Consecjuently, if the sternum were 

 inflexible (as it is in birds of powerful wing) in clavi- 

 cled birds which walk by striding with the alternate 

 foot, and not by hopping with both feet at once, the 

 line of the bird's body would twine about like a cork- 

 screw as it marched along, as the advance of each 

 foot would necessarily throw the anterior part of the 

 axis to the opposite side, and give the bird a swinging 

 motion upon its centre of gravity, which would con- 

 siderably increase the fatigue of walking, and thus be 

 a violation of that general law according to which all 

 the natural actions of animals are performed with the 

 smallest possible waste of their energy. We see 



