4 MAMMALIAN ANATOMY 



7. The Tegumentary, comprising the skin and its appendages, for 

 protection and excretion ; and the organs of the special senses, feel- 

 ing, seeing, hearing, smelling, and tasting, developed from it. 



The organs composing these systems are made up of tissues, 

 whereof the ultimate microscopic elements are the cells and the inter- 

 cellular substance, or matrix, whereby they are held together. 



There are five Tissues in the body : 



1. The Corpuscular, comprising the blood and lymph, with rounded 

 cells or corpuscles in a fluid matrix ; 



2. The Connective or supporting tissues, forming bones and car- 

 tilage and fibrous connections of all kinds ; 



3. The Epithelial, 1 limiting external and internal surfaces ; 



4. The Muscular, forming most of the flesh or muscles, and con- 

 tracting to produce motion ; 



5. The Nervous, comprising nerve-cells and nerve-fibres, for the 

 generation and transmission of nervous impulses. 



The organs of the body are composed of these different tissues in 

 varying proportions ; for example : bone is composed almost exclu- 

 sively of a special kind of connective tissue having a hard matrix ; 

 the muscles are largely muscular tissue bound together by fibrous 

 tissue, and penetrated by blood-vessels and nerves ; blood-vessels are 

 tubes of fibrous connective tissue, muscular tissue, and epithelial tissue ; 

 and the skin contains epithelial tissue, connective tissue, muscular 

 tissue, nervous tissue, and corpuscular tissue. 



An examination of tissues shows that their differences lie chiefly 

 in the form of the cells, in the character of the intercellular sub- 

 stance, and in the relations which exist between these cells and the 

 intercellular substance. Between these tissues there is another differ- 

 ence, and an extremely important one (not revealed by any microscope), 

 which is manifested by the functions of the tissues, or, in other words, 

 by the nature of the work which they perform. To understand these 

 differences in function we must understand the qualities or nature of 

 the single cell or egg from which the entire body is developed, or the 

 nature of a cell which remains functionally at the same stage of devel- 

 opment as the egg. Within the body such cells are the white cor- 

 puscles of the blood ; outside of the body, as independent animals, 

 they are called amoebae. When a white blood-corpuscle, or an amoeba, 



1 From (Gr.) epi, upon, and thele, a nipple, a papilla. 



