(lO THE CONNECTIVE TISSUES 



from a division, each may form matrix until they are separated into 

 lacunae and then divide in tin-n. Or a cell may divide to form two, 

 which remain in a common lacuna, and one or both of these may 

 divide again to form three or four. Different methods of division 

 may occur, and result in the production of other types of cell clusters. 

 The nuclei are rounded and relatively small. The cytoplasm 

 appears to be rich in fluid and in the dehydration necessary 

 for making permanent preparations it often shrinks far away 

 from the wall of the lacuna to which it is closely applied 

 during life. The matrix immediately surrounding the lacuna^ 

 is more basophilic than that more distant; this may be due to 

 the absence of the acidophilic collagenous fibers in this region, 

 or be associated with the fact that it is the most recently deposited 

 and may difYer slightly from the older material. Although embry- 

 onic cartilage increases by division of the chondrocytes within the 

 matrix, later growth is due mainly to formation of new cells and 

 cartilage on the periphery through the activity of the inner zone 

 of the perichondrium. The cells along the inner surface of 

 this sheath divide and differentiate to form young cartilage cells, 

 which in turn form matrix which separates them from the sheath 

 and adds to the cartilage mass. Blood vessels and nerves extend 

 into the outer portion of the perichondrium but not into the matrix, 

 so that nutritive materials received by the central cells must reach 

 them l)y diffusion through the matrix. 



Cartilage proper usually is markedly basophilic, but perichon- 

 drium takes acid stains. The intermediate region of developing 

 cartilage about the periphery shows a transition from the acid- 

 staining condition of the perichondrium to the basic staining matrix 

 of the inner region of the cartilage, indicating a chemical change 

 during development. Cartilage ])resent in some elasmobranchs 

 becomes calcified and forms a much harder and more rigid support 

 than the commoner hyaline cartilage. 



Elastic Cartilage. — In the fresh condition this type has a yellow 

 tinge due to the prominence of the elastic fibers in the intercellular 

 material. There is relatively little matrix aside from some forming 

 thin capsules about the cartilage cells. In this type the elastic 

 fibers form a coarse network continuing with the perichondrium. 

 Elastic cartilage occurs in the external ear of mammals and in the 

 smaller bronchi. 



Fibrous Cartilage. In this type there is an abundance of col- 

 lagenous fibers which form a network about the cartilage cells. 



