THE ANIMAL MACHINE 



Histology 



Fig. 1. — Glandular 

 epithelium. 



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- 

 tures such as the udder, are also 

 composed of epithelial tissue 

 (Fig. 1). 



8. Connective tissue. — The 

 connective tissue group com- 



FiG. 2. — Transverse section 

 of dried bone, h, one of the 

 Haversian canals, about 

 which the lamellce are con- 

 centrically disposed, consti- 

 tuting the Haversian sys- 

 tems ; g, the ground or in- 

 testinal lamellae. 



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