JOINTS 



of the fibrous type. These cartilages serve to deepen the sockets in which 

 the upper ends of the femur and h inner us move and are known as 

 adaptation cartilages or labra glenoidalia. 



The joint cavity of a diarthrosis is enveloped in a capsule consisting 

 of two layers, an outer fibre-elastic continuous with the periosteum and 

 an inner cellular layer, the synodal membrane, consisting of epithelioid 

 cells forming a mesenchymal epithelium. The function of the synovial 

 membrane is to secrete a lubricating fluid, the synovia, consisting of about 

 i>4 per cent, water with small amounts of mucoid substances and oil. 

 In the large joints the synovial (serous) membrane is thrown into villus- 

 like folds (Fig. 240). The covering cellular membrane is occasionally 

 imperfect; the cells vary from the flattened, typical mesothelial cells, to 

 the cubic variety (Fig. 44), and rest directly upon a vascular, frequently 

 fatty, fibrous stroma. 



