CARTILAGE. 251 



human body may be subdivided into three different sets. 1. 

 Those which at one period of life existed instead of the bones, 

 and which, after the bones are formed, constitute an essential 

 part of the bony texture. These have been already treated of 

 in the last two chapters. 2. Those cartilages which cover the 

 extremities of those bones which constitute moveable articula- 

 tions, and which are called cartilages of incrustation. These 

 cartilages are covered with a syuovial membrane which adds to 

 the polish of their faces. The greater and the more moveable 

 the articulations are to which these cartilages belong, the thicker 

 they are. In old age, these cartilages are occasionally converted 

 into bones. A portion of cartilage tipping the ileum bone of 

 an ox had a specific gravity of 1 '1521. 3. The cartilages which 

 unite the ribs to the sternum or to one another, those of the la- 

 rynx and of the nose, constitute the third set. They are cover- 

 ed by a fibrous membrane called perichondrium. They also (if 

 we except those of the nose) frequently ossify in old age; 



The facts respecting the structure of cartilages, so far as in- 

 vestigated, have been stated in the preceding chapters. They 

 seem, if we can confide in the microscopic observations of Pur- 

 kinje, Retzius, and Miiller, to consist of a congeries of very minute 

 tubes. When these tubes are filled with calcareous salts the 

 cartilages are converted into bone. It is evident from the dis- 

 eases to which cartilages are liable that they are supplied with 

 vessels. But in ordinary cases these vessels do not seem to con- 

 vey red blood ; though when inflammation intervenes they may 

 be occasionally seen filled with red blood. And such inflam- 

 mations may run the same career as in other organs. 



In the year 1827, Fromherz and Gugert* analyzed the carti- 

 lage of the ribs of a young man, aged 20 years, and found it, after 

 having been dried as completely as possible in the temperature 



(of 212, composed of, 

 Animal matter, . 96-598 

 Salts, . 3-402 



100-000 



The salts being subjected to an analysis were found composed 

 of, 



* Schweiger's Jour. 1. 188. 



