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trading head or knob, with a distinct convexity; and again presenting 

 a corresponding depression or cavity, accurately adapted to complete, 

 by their coaptation, the ball and socket joint. The articulation of the 

 arm and shoulder is an example of the first kind, while that of the 

 hip with the thigh bone is a perfect exhibition of the latter. 



The structure, whose oiiice is the retention of the articulation in 

 place, is the ligament. This is a white, inelastic, or yellowish texture, 

 possessing in some degree the opposite quality. In some instances it 

 is of a corded or funicular shape, but consists in others of a broad 

 membrane, in the first form serving to bind the bones more firmly to- 

 gether, and in the latter surrounding or inclosing, in whole or in part, 

 the broad articulations, aud calculated rather for the protection of the 

 cavity from intrusion by the air than for other security. These latter 

 are usually found in connection with those of the joints which possess a 

 free and extended movement, butare also found accompanying the funic- 

 ular ligaments either surronnding and inclosing the joints or occupy- 

 ing the interior of their structure, as inter articuJar, in which situation 

 they secure the union of the several bones more firmly and effectively 

 than would be possible for the capsular ligament unassisted. 



The universal need which pertains to all mechanical contrivances of 

 motion has not been forgotten while providing for the perfect working 

 of the interesting piece of living machinery which performs the func- 

 tion of locomotion, as we are contemplating it, and nature has conse- 

 quently i)rovided for obviating the evils of attrition and friction, and 

 insuring the easy play and smooth movement of its parts, by the estab- 

 lishment of the secretion of the synovia, the vital lubricant of which wo 

 have before spoken, as a yellow, oily, or rather glairy secretion, which 

 performs the indispensable ofiSce of facilitating the play of the tendons 

 over the joints and certain given points of the bones. This fluid, 

 which is deposited in a containing sac, the lining (serous) membrane of 

 which forms the secreting organ, is of an excessively sensitive nature, 

 and while it lines the inner face of the ligaments, both capsular aud 

 fascicular, is attached only upon the edges of the bones without extend- 

 ing upon their length or between the layers of cartilage which lie be- 

 tween the bones and their articular surfaces. 



Our object in thus partially aud concisely reviewing the structure 

 and condition of the essential organs of locomotion has been rather to 

 outline a sketch which may serve as a reference chart of the general 

 features of the subject, than to offer a minute description of the parts 

 referred to. Other points of interest will receive due attention as wo 

 proceed with the illustration of our subject and examine the matters 

 which it most concerns us to bring under consideration. The founda- 

 tion of facts which we have thus far prepared will be found sufficiently 

 broad, we trust, to include whatever may be necessary to insure a ready 

 comprehension of the essential matters which are to follow, as our re- 

 view is carried forward to completion. What we have said touching 

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