Chap. VIII 



EFFECTS OF USE AND DISUSE. 



299 



elongated. In the sternum, furcnlum, coracoids, and scapulae, the 

 differences are so slight and so variable as not to be worth notice, 

 except that in two skeletons of the Penguin duck the terminal 

 portion of the scapula was much attenuated. 



In the bones of the leg and wing no modification in shape could 

 be observed. But in the Penguin and Hook-billed ducks, the 

 terminal phalanges of the wing are a little shortened. In the 

 former, the femur, and metatarsus (but not the tibia) are con- 

 siderably lengthened, relatively to the same bones in the wild duck, 

 and to the wing-bones in both birds. This elongation of the leg- 

 bones could be seen whilst the bird was alive, and is no doubt 

 connected with its peculiar upright manner of walking. In a 

 large Aylesbury duck, on the other hand, the tibia was the only 

 bone of the leg which relatively to the other bones was slightly 

 lengthened. 



On the effects of the increased and decreased Use of the Limbs. — In 

 all the breeds the bones of the wing (measured separately after 

 having been cleaned) relatively to those of the leg have become 

 slightly shortened, in comparison with the same bones in the wild 

 duck, as may be seen in the following table : — 



Name of Breed. 



Wild mallard 

 Aylesbury . . 

 Tufted (Dutch) 

 Penguin 

 Call .. .. 



Length of Femur, 

 Tibia, and Meta- 

 tarsus together. 



Inches. 



•14 

 •64 

 •25 

 •12 



•20 



Length of Humerus, 

 Radius, and Meta- 

 carpus together. 



Or as 



100 : 129 

 100 : 120 

 100 : 119 

 100 : 123 

 100 : 125 



Wild duck (another speci- 

 men) 



Common domestic duck . . 



Length of same 

 Bones. 



Inches. 



6-85 

 8-15 



Length of all the 



Bones of Wing. 



Inches. 



10 



11 



07 

 26 



100 

 100 



147 



138 



In the foregoing table we see, by comparison with the wild duck, 

 that the reduction in the length of the bones of the wing, re- 

 latively to those of the legs, though slight, is universal. The 

 reduction is least in the Call duck, which has the power and the 

 habit of frequently flying. 



In weight there is a greater relative difference between the bonea 

 of the leg and wing, as may be seen in the following table : — 





