THE ANIMAL MACHINE 



9 



FIG. 1. Glandular 

 epithelium. 



HISTOLOGY 



6. Tissue. Any tissue is composed of an essential 

 unit of structure, the cell, and an inter-cellular material 

 by means of which the cells are held 

 together. The character of the cells 

 themselves, their arrangement in the 

 inter-cellular substance, its nature, and 

 the proportion of each are what give to 

 tissues their characteristic features. 



The animal body is composed of 

 four kinds of tissue, i.e. epithelial, con- 

 nective, muscle and nerve. The general 

 nature of each and its place in the 

 organization of the animal economy should be fully under- 

 stood in order to pass intelligently upon the relative struc- 

 tural and functional merits of two or more individuals. 



7. Epithelial tissue. The epi- 

 thelial group is represented by 

 the skin or outer covering of the 

 body; the mucous and serous 

 membranes lining the interior, 

 the former those cavities in com- 

 munication with the outside as 

 in the respiratory and digestive 

 tracts, the latter the closed cavi- 

 ties of the chest and abdomen. 

 The glands or secreting struc- 



FIG. 2. Transverse section 



of dried bone, h, one of the tures such as the udder, are also 



Haversian canals, about compose d O f epithelial tissue 

 which the lamellae are con- _ r 

 centrically disposed, consti- (Fig. 1). 



tuting the Haversian sys- g Connective tissue. The 



terns ; g, the ground or in- 

 testinal lamellae. connective tissue group com- 



