CHAPTER 3 



MORPHOLOGY OF THE VERTEBRATE BODY 



An understanding of scientific facts, in Zoology as in other 

 sciences, must rest upon a basis of first-hand knowledge. Little 

 knowledge is required for an understanding of the preceding chap- 

 ter, beyond the acquaintance with common animals that is pos- 

 sessed by most readers of a book of this character. In the present 

 chapter, more depends upon what the student may be presumed 

 to have seen in the laboratory, but he must also utihze such general 

 information as he may have concerning the structure of the human 

 body and that of familiar animals. As has been explained in the 

 introductory chapter, the various fields of biological science are 

 closely inter-related. This is particularly true of Morphology and 

 Physiology. The study of structure may interest us, because of 

 the intricacies or the beauties of form that it reveals; yet structure 

 never can become meaningful unless we possess some knowledge 

 of the way in which the parts work. The morphology of an auto- 

 mobile is interesting, but the parts have meaning only in relation 

 to their manner of action. For this reason, the present chapter, 

 which deals primarily with structure, will in many places explain 

 functions as well. Likewise, in Chapters 4 and 5, which deal with 

 functions, we shall find it necessary to explain structure in some 

 detail. All these chapters are intended to serve as a review and 

 extension of the knowledge concerning the functional organization 

 of the vertebrate body which is given in elementary textbooks of 

 human physiology, but which experience shows has not been prop- 

 erly comprehended by the majority of students before entering 

 upon the study of General Zoology. 



External Features and Related Structures 



Head, Body, Tail, and Appendages. — Reference has been 

 made in the preceding chapter to the external features of familiar 



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