CHAPTER IV 



THE- CONNECTIVE TISSUES 



THE connective tissues are the following : 



1. Areolar tissue. 6. Jelly-like tissue. 



2. Fibrous tissue. 7. Cartilage. 



3. Elastic tissue. 8. Bone and dentine. 



4. Adipose tissue. 9. Blood. 



5. Retiform and lymphoid tissues. 



At first sight these numerous tissues appear to form a very 

 heterogeneous group, including the most solid tissues of the body 

 (bone, dentine) and the most fluid (blood). 



But on examining a little more deeply, one finds that the group- 

 ing of these apparently different tissues together depends on a number 

 of valid reasons, which may be briefly stated as follows : 



1. They all resemble each other in origin. All are formed from 



the mesoblast, the middle layer of the embryo. 



2. They resemble each other structurally; that is to say, the 



cellular element is at a minimum, and the intercellular 

 material at a maximum. 



3. They resemble each other functionally ; they form the skeleton, 



and act as binding, supporting, or connecting tissues to the 

 softer and more vital tissues. 



An apology is sometimes made for calling the blood a tissue, 

 because one's preconceived idea of a tissue or texture is that it must 

 be something of a solid nature. But all the tissues contain water. 

 Muscular tissue contains, for instance, at least three-quarters^ of its 

 weight as water. Blood, after all, is not much more liquid than 

 muscle. Blood, moreover, contains cellular elements analogous to the 

 cells of other tissues, but separated by large quantities of a fluid 

 intercellular material called blood-plasma. 



Blood is also mesoblastic, and thus the two first characteristics of 

 a connective tissue are present. It does not fulfil the third condition 

 by contributing to the support of the body as part of the skeleton, 

 but it does so in another sense, and serves to support the body by 

 conveying nutriment to all parts. 



