194 The Bird 



animals. There are so many resemblances between birds 

 and reptiles that we naturally turn to the latter for com- 

 parison, but even here we find a great unlikeness. We 

 learned, when we reflected on the number of ribs of a 

 bird, that the repetition of so many similar structures 

 was merely the last remaining vestige of ancestral body 

 segments, which reach their extreme development (in 

 number and similarity) among the worms; but in regard 

 to muscles birds show little or nothing of this. In liz- 

 ards we may count dozens upon dozens of bands of muscles 

 succeeding one another, all more or less alike, from head 

 to tail, but it is only in the neck of a bird that we shall 

 find anything like this. 



In order to give to muscles a firm anchorage, they 

 must of course be attached to the bones. At these 

 points of attachment deep furrows or cavities are often 

 found in the surface of the bones, and in still other ways 

 we are reminded, even in fossil bones, of the flesh and 

 muscle which once moved them. These muscle impres- 

 sions are often a valuable source of identification in 

 naming the bones of creatures which, many thousands 

 of years ago, disappeared from the earth. And indeed 

 so great variety exists in the muscles of living birds that 

 many of them, those of the upper arm for example, are 

 of considerable value in classification. 



Nerves 



The last great system of internal organs which we 

 shall consider, and perhaps the most mysterious of all, 

 is that of the nerves. We have learned that the back- 



