58 



WINGLESS BIRDS. 



this species of insertion of the humerus in the large 

 clavicles and blade-bones. In those mammalia which 

 use the fore-legs for progressive motion only, there 

 are no clavicles, and bears and other hugging animals 

 have them cartilaginous at both extremities. So 

 that the absence of clavicles indicates motion in 

 the direction of the mesial plane only ; and their 

 presence, motion across that plane. 



Some of the birds which can fly, often use the half- 

 expanded wings to assist in balancing them when 

 they run ; and this habit is most frequent with those 

 that have the legs long. Some of the birds which 

 cannot fly, have rudimental wings, which they appear 

 to use for the same purposes. The only bird which 

 has the wings so perfectly rudimental and concealed 

 within the integuments as not to be of any use in 



Apteryx. 

 balancing, is the Apteryx : and it has the legs very 

 short and stout, and, though its habits are not known, 

 it is probably not much of a runner. 



Those short-winged birds which dive under water, 

 whether they tread the water itself by means of 

 webbed feet, as is the case with the di%ing ducks, 

 and divers properly so called, or tread the bottoms 



