CARTILAGE 



287 



Adipose Tissue. — Certain of the mesenchymal cells give rise not to fibro- 

 blasts but to fat cells. They seCrete within their cytoplasm droplets of fat which 

 increase in size and become confluent (Fig. 292). Finally, a single fat globule fills 

 the cell of which the nucleus and cytoplasm are pressed to the periphery. The 

 fat cells are most numerous along the course of the blood vessels in areolar con- 

 nective tissue and appear first during the fourth month. 



CARTILAGE 



Cartilage has been described as developing in two ways: (1) The mesen- 

 chymal cells "increase in size and form a compact cellular precartilage. Later the 



hyaline matrix is developed be- 



Mes. Precartilage 



Cartilage 



a'' .? 



'^M 







mm^mm^- 



Fig. 293. — Diagrams of the development of car- 

 tilage from mesenchyma (Lewis and Stohr). A, Based 

 upon Studnicka's studies of fish; B, upon Mall's study 

 of mammals. Mes,, mesenchyma. 



tween the cells from their cyto- 

 plasm (Fig. 293 A). The matrix 

 may in this case be regarded as 

 the ectoplasm of the cartilage 

 cells. (2) According'to Mall, mes- 

 enchymal cells give rise first to an 

 ectoplasm in which fibrilte de- 

 velop. Next, the cells increase in 

 size and are gradually extruded 

 until they he in the spaces of the 

 ectoplasmic matrix (Figs. 291 C 

 and 293 B) . Simultaneously, the 



ectoplasm is converted into the hyaline matrix peculiar to cartilage, undergoing 

 both a chemical and structural change. About the cartilage cells the endo- 

 plasm produces capsules of hyahne substance. 



The interstitial growth of cartilage is due: (1) to the direct production of new hyaKne 

 matrix; (2) to the formation of capsules about the cells arid their transformation into iflatfix; 

 (3) to the proliferation of the cartilage cells, which may separate or occur iri clusters within 

 a single capsule. 



Perichondral growth also takes place about the periphery of the cartilage and is due to 

 the activity of persisting mesenchymal cells, which, with an outer sheath of connective tissue, 

 constitute the perichondrium. When cartilage is replaced by bone the perichondrium 

 becomes the periosteum. 



In hyaline cartilage the matrix remains hyaline. In fibro-cartilage the fibrillations of the 

 primitive ectoplasm are converted into white fibers. In elastic cartilage yeUow elastic fibers 

 are formed in the hyaline matrix, according to Mall; before the hyahne matrix is differentiated, 

 according to Spalteholz. Most of the bones of the skeleton are laid down first in the form of 

 cartilage. Later, this is gradually replaced by the development of bone tissue. 



