CHAPTER IV. 

 THE CONNECTIVE TISSUES. 



The two varieties of elementary tissue that have just been con- 

 sidered — namely, endothelium and epithelium — owe their qualities 

 directly to the characters of the cells that enter into their composi- 

 tion. The intercellular substances are insignificant in amount and 

 subordinate in function. 



In marked contrast to these are the tissues composing the group 

 known as the " connective tissues." Here the usefulness of the 

 tissues depends upon the character of the intercellular substances 

 which confer upon the tissues their physical properties. The 

 activities of the cells entering into the composition of these tissues 

 appear to be confined to the production of those important inter- 

 cellular substances and the maintenance of their integrity. The 

 (•ells may, therefore, be considered as of secondary importance in 

 determining the immediate usefulness of the tissues, the first place 

 being 1 given to the intercellular substances. As was stated in the 

 introductory chapter, these connective tissues are essentially passive 

 — i. e., they are useful because of their physical characters rather 

 than because of any ability to transform either matter or energy. 

 Where the ability to accomplish those transformations is of 

 importance the tissues are found to be essentially cellular in char- 

 acter, as we have already seen to be the case in the epithelial tis- 

 sues. 



The connective tissues may be divided into three main groups : 

 the cartilages, bone, and the fibrous tissues. Each of these groups 

 has certain general structural characters that distinguish it from 

 the other elementary tissues, but within each group there are 

 varieties which differ considerably in the detailed character of their 

 intercellular substances and in the arrangement of these with re- 

 spect to the cells. 



All the elementary tissues belonging to the connective-tissue 

 group are developed from the mesoderm. 



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