COLLAGENOUS AND ELASTIC CONNECTIVE TISSUES 59 



stages of higher vertebrates. Tlie aiiioiiiit of the iiitercelhilar solid 

 matrix varies in many cases, but (h)es not far exceed the celhdar 

 components, as in cartihige. 



Cartihaginous tissue forms the entire skeleton of the elasmobranch 

 fishes, a considerable part of the skeleton of ganoid fishes, is still a 

 prominent element in the skeletal framework of amphibians, and, 

 though not so imi)ortant in the adult reptile, bird, and mammal, it 

 is the material of which the embryonic skeleton of these forms is 

 composed. Preliminary to cartilage formation, mesenchyme cells 

 accumulate and become compactly grouped until the original 

 stellate shape is lost. An intercellular substance, at first acidophilic 

 and then basophilic, forms together with collagenous fibrils. To 

 this point it resembles the chondroid tissue. By multiplicaticm 

 of the precartilaginous cells and increase in the intercellular material, 

 an irregular but comj^act mass is formed which compresses the sur- 

 rounding mesenchyme cells into the early form of perichondrium, 

 the peripheral sheath of cells and collagenous fibers active in forma- 

 tion of new cartilage cells, or chondrocytes, at the periphery. The 

 cells in the interior of the early cartilaginous mass divide, and the 

 newly formed cells in turn secrete about themselves more inter- 

 cellular matrix so that cartilaginous skeletal structures are formed. 

 The cells are usuall}' rounded and separated by matrix, but in some 

 cases cytoplasmic processes may extend through the matrix to 

 adjoining cells. On the basis of the composition t)f the intercellular 

 material, three types of cartilage are commonly distinguished, 

 namely, hyaline, elastic, and fibrous, although there are all grada- 

 tions from the early chondroid or embryonic condition to any of 

 the three named. 



Hyaline Cartilage. In living condition this widely distributed 

 type appears clear or slightly bluish and somewhat translucent. 

 When boiled, the matrix yields c-hondrin, a gelatinous material 

 resembling the gelatin obtained when collagenous fibers are boiled. 

 The ap])arently homogenous solid matrix may be dissolved by treat- 

 ing with trypsin and potassium permanganate and collagenous 

 fibers become apparent. It may be regarded as a specialized form 

 of dense fibrous connective tissue in which the matrix is a solid 

 organization of the intercellular tissue secretions. (Fig. 35.) 



Throughout the matrix cells occur in spaces termed lacuna^. 

 These cells, the chondrocytes, are closely related to the fibrocytes. 

 In embryonic cartilage, cells in the interior of the mass are still 

 active in mitotic division, and when in the two-cell stage resulting 



