OF THE COSTAL AND LARYNGEAL CARTILAGES. 353 



substance. All these divisions or separations are first pro- 

 duced at the circumference of the cartilage. The centre is 

 more homogeneous, and is the last part that divides. This 

 separation may be accelerated by drying in the sun a costal 

 cartilage that has been macerated for two or three months. 

 Acids produce a similar effect. 



560. The costal cartilages are somewhat flexible and high- 

 ly elastic. In inspiration, the motion impressed upon the ribs 

 by the muscles, bends them and twists them upon themselves; 

 and when the muscular action ceases, they spontaneously re- 

 sume their original direction, and are thus agents of expira- 

 tion. 



561. After adult age, and in old age, the costal cartilages 

 cease to be or to appear homogeneous. Their perichondrium 

 becomes opaque, and there are produced, between it and the 

 cartilage, and in its substance, bony plates, more or less nu- 

 merous and broad, which sometimes end with forming a more 

 or less complete bony sheath. This change almost always 

 happens to the first, commencing at its sternal extremity. The 

 other sterno-costal cartilages also experience it, but in a less 

 degree. The asternal costal cartilages, or those of the false 

 ribs, experience it still less, or not at all. At the same time 

 the costal cartilages become yellowish, then reddish in their 

 centre, which also presents more or less large and numerous 

 bony points, which sometimes at length occupy the whole car- 

 tilage. This latter phenomenon shows itself more frequently 

 and sooner in the asternal cartilages than in the others. 



These changes in the cartilages are commonly the effect of 

 age. They commence towards the middle of life, and go on 

 continually increasing. Persons of a hundred and thirty and 

 a hundred and fifty years, however, have been seen to have 

 costal cartilages in their natural state. 



When the cartilages begin to undergo this change, desicca- 

 tion causes them to break across in the centre, which has be- 

 come areolar, and not at the surface, which has, on the con- 

 trary, become denser. 



They frequently ossify, and at an early age, in persons 

 affected with phthisis, 



