552 ELEMENTARY PHYSIOLOGY less. 



definitely limited possibilities of growth and metamor- 

 phosis are inherent, as they are in those equally simple 

 organisms, the spores of the conunon moulds, Penicilliuvi 

 and Mtccor. Given the proper external conditions, the 

 latter grow into moulds of two diffei'ent kinds, while the 

 former grow into cartilage and horny plates. 



(ii) TVhite Fibro-Cartilage. — Since cartilage is a tissue 

 which serves chiefly for the purposes of supporting 

 and connecting other structures of the body, it requires, 

 in certain positions, to be somewhat more tough and re- 

 sistent, less brittle and more flexible than in others. 

 Thus in some joints, as for instance the knee, there are 

 little pads or discs of cartilage between the ordinary 



Fia. 179. — Section of Yellow Elastic Cartilage. (HARDr.) 



articular cartilage (see Fig. 97, c). Similar discs lie in 

 between and are attached to the bodies of the vertebrae. 

 They act not only as a sort of cushion to break the "jar " 

 arising from a sudden concussion of the vertebral column, 

 but also bind the vertebrte into a column which is re- 

 sistent but at the same time flexible. The additional 

 strength required by the cartilages of these discs is pro- 

 vided by the introduction into their matrix of bundles of 

 white fibrous connective tissue ; hence the name, white 

 tibro-cartilages (Fig. 178). 



(iii) Yellow or Elastic Fibro-Cartilage. — In certain 

 other parts of the body cartilage is required to be pecu- 



