TENDON 



77 



may contain a cavity filled with fluid. It is then called a mucous sheath 

 or vagina mucosa. The cavity arises as a cleft in the embryonic connective 

 tissue and its walls are formed of mesenchymal epithelium. The cells 

 have become flattened and the fibers felted together to bound the space. 

 It contains a fluid like that of the joint cavities, being chiefly water and 

 a mucoid substance which renders it viscid, together with protein material 

 and salts. The function of the mucous sheath is to facilitate the move- 

 ments 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 

 burs<z 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, fasciae and ligaments are connective tissue formations, 

 resembling tendon in possessing a more or less regular arrangement of 

 cells and fibers. Elastic elements may be abundant. 



Mes. 



Pre.Cart. 



Cart. 



CARTILAGE. 



Cartilage is a mesenchymal derivative, the development of which it 

 is difficult to follow, since at certain stages its nuclei are so crowded that 

 they obscure the transformation of the intercellular substance. Two 

 interpretations of its develop- 

 ment are illustrated in Fig. 

 66, A and B. As represented 

 in A, the mesenchymal cells 

 multiply and come together so 

 that the intercellular spaces 

 are obliterated. Thus pre- 

 cartilage is formed, consisting 

 of large closely adjacent cells, 

 separated from one another by 

 thin walls which stain red 

 with eosin. This type of pre- 

 cartilage has been frequently 

 described in the lower verte- 

 brates. It becomes cartilage by the thickening and chemical transforma- 

 tion of its exoplasmic walls. They form an intercellular ground sub- 

 stance or matrix, which stains blue with haematoxylin. According to 

 Professor Mall the same result is produced in another way, as shown in 

 Fig. 66, B. The mesenchymal cells in becoming precartilage produce a 

 fibrillated exoplasm. The nuclei with the surrounding endoplasm then 

 become "extruded from the syncytium" and lie in the intercellular spaces. 



FIG. 66. DIAGRAMS OF THE DEVELOPMENT OF CARTILAGE 



FROM MESENCHYMA. 



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

 study of mammals. Mes.. Mesenchyma; Pre. Cart. 

 precartilage; Cart., cartilage. 



