Chap. V. ON THE EFFECTS OF DISUSE. 175 



This table shows that in these twelve breeds the sternum is on an average 

 one-third of an inch (exactly -332) shorter than in the rock-pigeon, pro- 

 portionally with the size of their bodies; so that the sternum has been 

 reduced by between one-seventh and one-eighth of its entire length ; and 

 this is a considerable reduction. 



I have also measured in twenty-one birds, including the above dozen, 

 the prominence of the crest of the sternum relatively to its length, inde- 

 pendently of the size of the body. In two of the twenty-one birds the 

 crest was prominent in the same relative degree as in the rock-pigeon ; in 

 seven it was more prominent ; but in five out of these seven, namely, in a 

 fantail, two scanderoons, and two English carriers, this greater promi- 

 nence may to a certain extent be explained, as a prominent breast is 

 admired and selected by fanciers; in the remaining twelve birds the 

 prominence was less. Hence it follows that the crest exhibits a slight, 

 though uncertain, tendency to become reduced in prominence in a greater 

 degree than does the length of the sternum relatively to the size of body, in 

 comparison with the rock-pigeon. 



I have measured the length of the scapula in nine different large and 

 small-sized breeds, and in all the scapula is proportionally shorter 

 (taking the same standard as before) than in the wild rock-pigeon. The 

 reduction in length on an average is very nearly one-fifth of an inch, 

 or about one-ninth of the length of the scapula in the rock-pigeon. 



The arms of the furcula in all the specimens which I compared, diverged 

 less, proportionally with the size of body, than in the rock-pigeon ; and the 

 whole furcula was proportionally shorter. Thus in a runt, which measured 

 from tip to tip of wings SSh inches, the furcula was only a very little 

 longer (with the arms hardly more divergent) than in a rock-pigeon which 

 measured from tip to tip 26i inches. In a barb, which in all its mea- 

 surements was a little larger than the same rock-pigeon, the furcula was 

 a quarter of an inch shorter. In a pouter, the furcula had not been 

 lengthened proportionally with the increased length of the body. In a short- 

 faced tumbler, which measured from tip to tip of wings 24 inches, therefore 

 only 2£ inches less than the rock-pigeon, the furcula was barely two-thirds 

 of the length of that of the rock-pigeon. 



We thus clearly see that the sternum, scapula?, and furcula 

 are all reduced in proportional length; but when we turn to 

 the wings we find what at first appears a wholly different 

 and unexpected result. I may here remark that I have not 

 picked out specimens, but have used every measurement made 

 by me. Taking the length from the base of beak to the end 

 of the tail as the standard of comparison, I find that out of 

 thirty-five birds of various breeds, twenty-five have wings of 

 greater, and ten have them of less proportional length, than in 

 the rock-pigeon. But from the frequently correlated length of 

 the tail and wing-feathers, it is better to take as the standard 



