PAKT I. THE BABBIT. 



CHAPTER I. INTRODUCTORY. 



1. External Form. It is unnecessary to enter upon a 

 description of the appearance of this familiar type, but it 

 is not perhaps superfluous, as we proceed to consider its 

 anatomy, to call attention to one or two points in its ex- 

 ternal, or externally apparent, structure. Most of our 

 readers will already know that it belongs to that great 

 division of the animal kingdom which is called the Vertebrata, 

 and that the distinctive feature which places it in this 

 division is the possession of a vertebral column or backbone; 

 really a series of small ring-like bones, the vertebrae, strung 

 together, as it were, on the main nerve-axis, the spinal 

 cord (fig. 1). This vertebral column can be felt along the 

 neck and back to the tail. This tail is small, tilted up, 

 and conspicuously white beneath, and it serves as a 

 "recognition mark " to guide the young when, during feed- 

 ing, an alarm is given and a bolt is made for the burrows. 

 In those more primitive (older and simpler-fashioned) 

 vertebrata, the fishes, the tail is much larger and far more 

 important, as compared with the rest of the body, than 

 it is in most of the land-inhabiting vertebrates. In the 

 former it is invariably a great muscular mass to propel 

 the body forward ; in the latter it may disappear, as in 

 the frog, be simply a feather-bearing stump, as in the 

 pigeon, a fly-flicker, as in the cow or horse, a fifth hand, as 

 in some monkeys, an emotional index, as in the dog, or be 

 otherwise reduced and modified to meet special require- 

 ments. 



2. Divisions of the Body. At the fore end, or, as 

 English zoologists prefer to say, anterior end, of the 

 ZOOL. 1 



