258 THE STRUCTURE AND LIFE OF BIRDS chap. 



certain point, its lower face looking backward, the effect 

 will be the same, without the help of the Latissimus. 

 During the upstroke the hind-quarters drop no more 

 than the rest of the body. The centre of gravity 

 is always behind the shoulder ; in fact, when the 

 hinder part of the body is raised, it retreats still further. 

 It ought not to fall in a vertical line between the points 

 of the wings' attachments any more than a skater's 

 centre of gravity, when he describes a curve, ought to 

 be directly over his skate. The action of the wings, 

 nicely regulated by the Latissimus, is to raise the 

 hinder and lower the anterior part of the body, and, if 

 the bird were balanced horizontally between them, 

 would send him heels over head. The fact that the 

 main weight is behind prevents this, and enables him 

 to choose his course. 



If an animal uses for progression at one time his 

 fore limbs only, at another his hind limbs, the centre of 

 gravity question cannot fail to be interesting, as equi- 

 librium must be maintained under two different sets of 

 circumstances. How well the point is situated for 

 flight, I have shown. In standing or walking, the 

 thigh-joint is a long way behind the main bulk of 

 the body, and the long toes are necessary to give 

 support at the required point. The horizontal or 

 nearly horizontal carriage of the body calls into play 

 muscles which, passing from the posterior end of 

 the pelvis to the thigh-bone, pull the hind-quarters 

 downward, and so raise the head and shoulders. The 

 more upright the bird, the farther back the centre of 

 gravity, and the less the pressure upon the toes. 

 When standing, a bird is in the position of a man who 



