THE GENERAL STRUCTURE OF JOINTS 107 



The ligaments are mainly white fibrous tissue of 

 various forms, serving to connect the articular surfaces 

 of bones; and the fibers, usually arranged in parallel 

 rows, or closely interlaced with one another, present 

 a white, shining, silvery surface, when seen in the 

 recent state. Some ligaments contain yellow elastic 

 tissue, which is present in the ligamentum subflava 

 connecting the adjacent arches of the vertebrae in man. 



The Synovial Membrane. This is a thin, delicate 

 serous membrane arranged like a short white tube, 

 attached by its open ends to the margins of the artic- 

 ular cartilages and covering the inner surfaces of the 

 various ligaments, so that along with the cartilage it 

 completely encloses the joint cavity. It secretes a 

 viscid, thick fluid like the white of an egg hence its 

 term synovia which acts as a lubricant to the joint. 

 The membrane is composed of a layer of endothelial 

 cells resting upon a thin layer of fibro-elastic (sub- 

 endothelial) tissue. There are three varieties of sy no- 

 vial membranes articular, bursal, and vaginal. 



The articular is found in a freely movable joint. It 

 lines the capsule and the non-articular intracapsular 

 portion of the bones which enter into the formation of 

 a joint. Some of these membranes contain fat, acting 

 as a cushion between the articular surfaces. 



The bursse are mucous between the skin and bone 

 (subcutaneous synovial bursae) ; and synovial between 

 muscles, tendons, and bone (subtendinous synovial 

 bursse) . 



Vaginal synovial membranes are sheaths for tendons. 

 They prevent friction and with their secretion lubricate 

 the tendons as they move within the sheath in carry- 

 ing on their action. 



Some joints have tendons passing through their 

 cavities (the knee-joint has the popliteus muscle and 

 the shoulder-joint the biceps) and they are always 

 enclosed by the synovial membrane within the joint, 

 to prevent friction and facilitate action. 



