xiv INTRODUCTION 



might be wearisome to those who are not partictilarly 

 interested, but we may indicate the nature of the argu- 

 ment by a comparison of the hind limb of the bird and 

 reptile. This limb, in both, is peculiar in that the 

 ankle-joint is formed in such a tvay that when the 

 foot is bent the joint turns on a hinge formed between 

 two rows of ankle-bones, while in mammals the 

 joint is formed by the hinging of the shank of the 

 leg upon the uppermost row of ankle-bones. But the 

 bird's leg is peculiar in that these two rows of ankle- 

 bones have undergone great modifications, and can be 

 seen in their originally separate condition only by ex- 

 amining the chick some time before hatching, though 

 traces yet remain in a young fowl of, say, three months 

 old (see Fig. 1). It is owing to the fact that these 

 peculiarities are not generally known, that most books 

 on birds are inaccurate when they describe the "legs 

 and toes" of a bird, the legs being the long "cannon- 

 bones," which are clad in scales and often brightly 

 coloured. 



A reference to the accompanying diagram should 

 make this clear. Here we have the leg of a fowl. 

 The first joint is formed by the hinging of the femur, 

 or thigh-bone, with the tibia, thus forming the "knee- 

 joint." At the end of the tibia is the joint with the 

 ankle-bone ; but in the birds, as we have said, the two 

 rows which these small bones make up disappear be- 

 fore adult life is reached. One row (shown in 

 Fig. 1), composed in the half-grown bird of a mallet- 

 like piece, the handle of which runs up the front of 

 the tibia or shank, becomes welded to the "shank"; 

 while the other ("2nd Row," Fig. 1), composed of 



