THE CONNECTIVE TISSUES. 



35 



CHAPTER III. 



THE CONNECTIVE TISSUES/ 



THE important group of connective substances the most widely 

 distributed of all tissues is the direct product of the great meso- 

 blastic tract, axial as well as peripheral ; the several members of this 

 extended family are formed by the differentiation and specialization 

 of the intercellular substance, wrought through the more or less 

 direct agency of the mesoblastic cells. The variation in the physical 

 characteristics of these substances is due to the condition of the 

 intercellular constituents of the tissues. Taken during the period 

 of embryonal growth, they are represented by a semi-gelatinous, 

 soft, plastic mass ; a little later, the still soft, but already definitely 

 formed, growing connective tissue exists, which is soon replaced by 

 the yielding, though strong, adult areolar tissue. Grouped as masses 

 in which the white fibrous tissue predominates, the marked tough- 

 ness of tendon is reached ; or where large quantities of yellow elastic 

 tissue are present, great extensibility is secured. A further conden- 

 sation of the intercellular substance produces the resistance of the 

 matrix of hyaline cartilage, with the intermediate gradations pre- 

 sented by the fibrous and elastic varieties ; the ground-substance 

 becoming additionally impregnated with calcareous salts, the well- 

 known hardness of bone or dentine is attained. In all these varia- 

 tions in the density of the intercellular substance the cells have 

 undergone but little change the connective-tissue corpuscle, the 

 tendon-cell, the cartilage-cell, and the bone-corpuscle being morpho- 

 logically identical. 



The principal forms in which connective tissue occurs are, 



1 . Mucous tissue, as in the jelly of Wharton of the umbilical cord. 



2. Growing, immature tissue, as in very young animals or in old 

 embryos. 



3. Areolar tissue, as in the subcutaneous and intermuscular tissues. 



4. Dense mixed fibrous and elastic tissue, as in the sclera, fasciae, 

 etc. 



5. Dense white fibrous tissue, as in tendon and the cornea. 



6. Dense elastic tissue, as in the ligamenta subflava. 



7. Cartilage fibrous, elastic, and hyaline varieties. 



8. Bone. 



9. Dentine. 



10. The reticulum of adenoid tissue and glands. 



