THE BONES AND JOINTS. 753 



Fibroma occurs as an hypertrophy of the little tufts and fringes of the 

 synovial membrane. In this way large polypoid and dendritic bodies 

 are formed. The pedicles of these growths may atrophy and even dis- 

 appear, so that the growths are left free in the cavities of the joints. 



Corpora aliena Articulorum (Loose Cartilages in the Joints). This name 

 is given to bodies, of various structure and origin, which are found free 

 or attached by slender pedicles in the cavities of the joints. They are 

 most frequently found in the knee ; next in order of frequency in the 

 elbow, hip, ankle, shoulder, and maxillary joints. They may be single 

 or in hundreds. Their size varies from that of a pin's head to that of 

 the patella. They are polypoid, rounded, egg-shaped, or almond- 

 shaped ; their surface is smooth or faceted, or rough and mulberry-like. 

 They are composed of fibrous tissue, cartilage, and bone in various pro- 

 portions. 



These bodies are formed by hyperplasia of the synovial tufts and 

 the production in them of cartilage and bone. 



More frequently the small plates of cartilage form on the inner surface 

 of the synovial membrane, which increase in size while their outer layers 

 ossify. These may remain fixed in the synovial membrane ; or they pro- 

 ject and become detached from it, and they then appear as flattened, 

 concave bodies composed of bone covered with cartilage on one side. 



On the other hand, cartilage and bone may form outside the synovial 

 membrane from the periosteum or the edges of the articular cartilages, 

 and pushing inward, may later become detached. 



Earely portions of the articular cartilages may be detached by vio- 

 lence or disease ; or fibrinous and other concretions may form in arthri- 

 tis, or under conditions which we do not understand. ' 



1 For a detailed consideration of lesions of the bones and joints consult Zieyler, 

 "Lehrbuch der Pathologic," vol. ii. 

 48 



