CHAPTER IV 

 CARTILAGE 



CARTILAGE is a dense, firm, but elastic substance, resembling 

 connective tissue in that it is developed from similar mesoblastic 

 cells. It contains a ground substance, the cartilage matrix, and 

 at times fibres, which may be either white fibres or yellow elas- 

 tic. The presence, absence, or character of these fibres determines 

 the variety of cartilage. Three varieties are thus distinguished : 

 hyaline cartilage, in which no fibres can be demonstrated within 

 the matrix ; elastic cartilage, whose matrix is permeated by yellow 

 elastic fibres; and fibrocartilage, whose matrix contains white 

 fibers. 



HYALINE CARTILAGE. This is the most abundant of the 

 three varieties. It is found in the respiratory system, forming the 

 cartilages of the nose, larynx, trachea, and bronchial tubes; in 

 the costal cartilages of the ribs; as articular cartilages cover- 

 ing the ends of long bones ; and in embryo, where, in the 

 course of development of the bones, the entire skeleton, except- 

 ing only the flat bones of the skull and face, at .first consists 

 of hyaline cartilage. In most of these locations the cartilage 

 occurs as plate-like masses, which are surrounded or encapsulated 

 by a vascular membrane of dense fibrous and ^elastic tissue. This 

 membrane is the perichondrium. The inner portion of this mem- 

 brane is richly supplied with small cells, and it is from this cell 

 layer that the cartilage is presumably developed. These chondro- 

 genetic cells multiply, and deposit about themselves the structure- 

 less mass which first forms merely a capsule to the cell, but which, 

 as it increases in amount, separates the various cells by wider areas 

 and becomes the cartilage matrix. The cells, which in the perichon- 

 drium are small and decidedly flattened, likewise increase in size 

 during this process, and become more nearly spherical, so that 

 those cartilage cells which lie near the center of the cartilaginous 

 plates are spheroidal in shape, while those toward the surface are 

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