206 DISEASES OF THE JOINTS. 



hair around its borders well saturated with grease, and the 

 blister carefully applied to the clipped patch only, no danger 

 may be apprehended. It should, however, be washed off at the 

 end of twenty-four hours. 



The diathrodial or true joints are divided into three varieties, 

 namely, arthrodia or gliding joints, the enarthrodia, and the 

 ginglymoid. 



The arthrodia are liable to inflammation, and ulceration of the 

 articular surfaces, arising primarily in the bones entering into 

 their conformation. 



The enarthrodia, or ball-and-socket joints, are in our patients 

 seldom diseased, and generally the cause of such disease arises 

 intrinsically, such as from the rheumatoid or the tubercular 

 diathesis. They are clothed by muscular tissue, and but rarely 

 suffer from accidents. 



The ginglymoid or hinged joints are exposed to injuries from 

 without, such as sprains and punctures, which are productive of 

 a variety of diseases, namely, inflammation of the synovial mem- 

 brane (acute and chronic), destruction of the articular cartilage, 

 caries of the extremities of the bones, a deposition of calcareous 

 matter in their structure, called the porcellaneous deposit, loose 

 bodies in the synovial cavity, defective secretion of synovia, in- 

 creased secretion of it, constituting dropsy of the articulation, 

 and anchylosis ; these are also liable to be accidentally opened. 



When inflammation of a joint arises from a strain, the liga- 

 ments are not only stretched, but are more or less lacerated at 

 their points of attachment. These ligaments, it will be re- 

 membered are lined upon their unattached internal surfaces 

 by synovial membrane, which becomes inflamed when they are 

 strained, and from these points the inflammation extends along 

 the whole synovial surface of the articulation. 



The true hock-joint, namely, that constituted by the tibia 

 and astragalus, may be taken as a type in our description of 

 these various forms of pathological changes. 



INFLMIIVIATION OF THE SYNOVIAL MEMBRANE, OR 

 ACUTE SYNOVITIS. 



The primary effects of inflammation upon this membrane are 

 more or less injection of the vessels, opacity, and dulness of its 



