CHAPTER II. 



THE CONNECTIVE TISSUES. 

 BY A. ROLLETT, 



PROFESSOR OF PHYSIOLOGY IN GRAZ. 



IT has become customary in histology to associate together a 

 series of tissues under the term connective tissues. From these 

 tissues all those portions of the animal body are formed, which 

 can be regarded in the most general significance of the terms 

 as the basement membrane, supporting layer or investment for 

 epithelial structures, blood, lymph, muscles, and nerves. In the 

 Vertebrata the group of connective substances includes connec- 

 tive tissue, cartilage, bone, the tissue of the cornea and dentine. 

 The connective tissues are developed from the middle ger- 

 minal layer, in which blood and muscle also originate. The 

 typical connective substances are recognised histologically by 

 the circumstance that they contain extensive and continuous 

 layers of material (intercellular substance), which, when com- 

 pared with the cellular structures distributed through its 

 substance (protoplasma), or the morphological elements in 

 other tissues, always appears as a more passive substance, 

 and one which participates but slightly in the processes cha- 

 racteristic of life. These masses consist for the most part of 

 gelatine-forming substances, such as collagen, chondrogen, and 

 ossein. The connective tissues frequently pass by substitution 

 or genetic succession into one another ; they appear therefore to 

 be morphologically equivalent ; so that in many instances cer- 

 tain organs, or parts of organs, belonging to animals nearly 

 allied to one another, are formed sometimes of one, sometimes 

 of another of these tissues. 



