14 BRITISH BIRDS 



between these two bones is, in flying birds, a considerable one, but 

 in the ostrich tribe they are almost in the same straight line ; 

 this is really connected with the power of flight, for it has been 

 shown by careful measurements that, in birds which still have 

 wings that bear every appearance of being functional, and yet are 

 not used for their legitimate purpose, the angle tends to approach 

 the obtusity of the scapula and coracoid of the Ostrich. Birds 

 have, besides these two bones, the merr3 T -thought, or cl;i \iclc 

 (58, fig. 8), which corresponds to our collar-bone. Its two halves are 

 generally closely united to form one U-shaped or V-shaped bone ; 

 but sometimes they are separate, and then more or less rudimentary. 



Wing. 



We must enter into the matter of wing a little more closely it 

 is so important a feature of bird organisation. The wing, of course, 

 although it performs so different a role, is the exact equivalent of 

 the fore limb of mammals. We can easily recognise precisely the 

 same bones, though they are diminished in number, and often of a 

 different form. It will be noticed that in each case we can dis- 

 tinguish the three bones forming the arm, and which are known as 

 the humerus, the radius, and ulna. The rest of the limb in the bird 

 is not quite so obviously like the hand of the mammal ; but a 

 little attention wih 1 show that it is constructed upon a perfectly 

 similar plan. The flexible wrist of the mammal is made up of many 

 small bones ; the hand itself is made up of a larger series still, of 

 which those nearest to the wrist are technically termed the meta- 

 carpals, and those which follow, the phalanges. In many mammals 

 there are five fingers ; but there are many which have less, and the 

 extreme is reached in the horse, which has to put up with a single 

 finger and small rudiments of two others. Now the bird is better 

 off in the way of fingers than the horse, as it has three fairly well- 

 developed fingers, or rather two well developed and one less perfect. 

 The shortest finger corresponds to the thumb of our hand. It is 

 more freely movable than the others. The metacarpal bones of the 

 second and third fingers are firmly welded together, and are long ; 

 each finger (as will be seen from a look at fig. 1, p. 4) has one 

 or two phalanges, as the case may be. Now in mammals the end 

 phalanx of each finger is tipped with a nail, or with a hoof. The 

 powerful claws of the tiger, used for tearing, and the solid hoof 



