5 



HISTOLOGY. 



the space. It contains a fluid like that of the joint cavities, being chiefly 

 water and a mucoid substance (not a true mucin) which renders it viscid, 

 together with proteid and salts. The function of the mucous sheath is 

 to facilitate the movements of the tendon. By its formation the tendon 

 is freed from the local connection with surrounding tissue, and the sheath 

 generally occurs where such connection would especially interfere with 

 motion. The mucous bursae are similar structures in relation with muscles 

 or bones. The joint cavities, to be described later, belong in the same class, 

 having a similar origin and function. 



Aponeuroses and fasciae are connective tissue formations, resembling 

 tendon in possessing a more or less regular arrangement of cells and 

 fibers. Elastic elements may be abundant. 



CARTILAGE. 



Cartilage is a derivative of mesenchyma which may develop as shown 

 in Fig. 54, A. The mesenchymal cells multiply and become crowded 



Cart together so that the inter- 



cellular spaces are obliter- 

 ated. Thus precartilage is 





FIG. 54. DIAGRAMS OF THE DEVELOPMENT OF CARTILAGE 

 FROM MBSENCHYMA. 



A, Based upon Studnicka's studies of fish; B, upon Mall's 

 study of mammals. Mes., Mesenchyma ; Pre. Cart., pre- 

 cartilage; Cart., cartilage. 



formed, consisting of large 

 closely adjacent cells sepa- 

 rated from one another by 

 thin walls staining red with 

 eosin. Precartilage becomes 

 cartilage by the thickening 

 of these exoplasmic walls 

 which become changed 

 chemically so that they stain 

 blue with haematoxylin. 

 The endoplasm may shrink 

 from them so that the cell is seen to occupy a little cavity in the 

 exoplasmic matrix. The cavity is a lacuna and if the matrix around it 

 appears to form a special wall for the lacuna, the wall is called a capsule. 

 The cell is the center of matrix formation, producing it in concentric 

 layers; and the capsule, being that portion of the matrix. nearest the cell, 

 is the part most recently formed. The cells consist of a spongy protoplasm 

 due to vacuoles of fat, and to spaces from which glycogen has been removed. 

 Within a lacuna the cells may divide by mitosis so that there may be four 

 or eight in one capsule. Ordinarily they move apart, by resorbing the 

 adjacent matrix (Stohr) or by forming new ground substance which forces 

 them apart (Mall). New exoplasmic walls develop between them, pro- 



