72 HISTOLOGY. 



fibrils of the perichondrium change into the ground substance 

 of the cartilage and the connective-tissue cells into cartilage 

 cells. The ground substance undergoes, in age, senile changes. 

 such as the so-called asbestos change, calcification, and bone 

 formation. 



The first change, which may be recognized by the naked 

 eye, produces in the cartilage areas which have somewhat the 

 appearance of asbestos. The process usually begins in the 

 ground substance by a production of fibres arranged in parallel 

 lines. These have nothing to do with the essential fibrillar 

 structure of the ground substance. They appear first at a 

 distance from the capsules, and proceed on every side toward 

 these, which also in time suffer change. They spread slowly 

 over the whole cartilage, and give it a white appearance. The 

 fibres do not swell up in acetic acid, but dissolve in dilute solu- 

 tions of sodium hydroxide and on boiling. 



Calcification, on the other hand, begins with the deposition 

 of granules of calcium carbonate in the ground substance in the 

 neighborhood of the capsules. This spreads throughout the 

 ground substance, and appears white in reflected light and 

 black in transmitted light. The granules dissolve in hydro- 

 chloric acid, giving rise to bubbles of carbon dioxide. This 

 change takes place especially in the laryngeal, tracheal, and 

 costal cartilages, which become in consequence opaque and 

 hard. 



Ossification of cartilage takes place as age advances. Its 

 first stage is marked by an ingrowth of blood-vessels from the 

 perichondrium (see Bone Development). 



Hyaline cartilage is found temporarily in embryos in places 

 where bone is to be formed. Permanently it occurs in the 

 cpiplivses and the joint cartilages. Also, it forms a large part 

 of the laryngeal, tracheal, and bronchial cartilages. It is 

 found in the nose, the ribs, and in all symphyses arid synchon- 

 droses. 



(b) Elastic Cartilage. Here the ground substance contains 

 a greater or smaller number of elastic fibres, which vary greatly 

 in thickness and show a marked tendency to branch and form 



