COMPAKATIVE ANATOMY. 



INTRODUCTION. 



I. ON THE NATURE AND MEANING OF COMPARATIVE 



ANATOMY. 



A THOROUGH knowledge of the animal body cannot be gained 

 by Comparative Anatomy alone, and it is therefore necessary to 

 call in the aid of other branches of science also, viz. : 



1. Ontogeny; 2. Palaeontology; 3. Histology; and 4. 

 Physiology. 



The first of these treats of the developmental history of the 

 individual, while the second has to do with the development of 

 the races of animals in time (Phylogeny). As the different 

 phases of development of the race are usually repeated to a 

 greater or less extent in those of the individual, these two subjects 

 help to complete one another. Thus the object of both alike is 

 to enable us to ascertain the past by observing the present. 



The third-mentioned branch, Histology, teaches us about the 

 structural elements the building-stones of the organism. It 

 shows how these elements are combined to form tissues, and how 

 organs are constructed out of the latter. The organs again 

 combine to form systems of organs. 



The structural elements consist primarily of cells and second- 

 arily of cells and fibres, and the different tissues may be divided 

 into four principal groups : 



1. Epithelium, and its derivative, glandular tissue. 



2. Supporting-tissue (connective-tissue, cartilage, bone). 



3. Muscular tissue. 



4. Nervous tissue. 



In accordance with their physiological character, epithelium 

 and supporting-tissue maybe described as passive, and muscular 

 and nervous tissue as active. 



E 



