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tremities of its movements — the latter more especially regulating the 
movements themselves, and presenting the greatest extent of sur- 
face, which again consists of a moiety for each half of the movement, 
the one portion breaking contact, while the other is acting, and vice 
versa. 
3. Even the acting facets of opposite articular surfaces are only 
congruent at one particular stage of their movement. 
4. The movements of opposite diarthrodial surfaces upon one 
another appear to be in every instance a combination of gliding and 
rolling — the amount of the former being directly, and that of the lat- 
ter inversely, as the congruence of the opposite articular surfaces. 
Referring to the important simultaneous discovery recently made 
by Langer and Henke, and verified by Meissner, of the screwed 
structure of certain joints, the author proceeded to state, that he 
would in a future communication on the ancle and tarsal joints give 
the grounds on which he had come to the conclusion, 
1. That in all the joints hitherto examined the screw is developed 
on a conical surface, and not on a cylindrical one, as is held by Langer 
to be generally the case. 
2. That not only is it impossible accurately to prolong the screwed 
surface by uniting longitudinally a number of casts made from it, 
but that neither the original surface nor its cast admits of being 
screwed along the mould, with continued congruity of surface. 
3. That this incongruity depends, in the first place, on the screwed 
surface being conical, and on the rapid increase in the obliquity of 
the thread ; and, in the second, on its consisting of at least two 
areas, each being a portion of a conical screw. 
After exhibiting prolonged screws, made according to Langer’s 
method, from the upper articular surface of the astragalus in the horse, 
panther, lion, and human subject, the author proceeded to state, that, 
induced to re-examine the knee-joint from this fresh point of view, 
he had ascertained, in the first place, that the path described by any 
point in the thigh, when the leg is fixed, and the knee put through 
its movements, does not lie in the presumed plane of flexion and ex- 
tension, as it would do if the profile curvatures of the femoral con- 
dyles were circular arcs, or logarithmic spirals, according to the 
ordinary view, or that of the brothers Weber; neither does the 
point in the upper part of its course describe the arc of a circle in 
a plane oblique to that in which it must afterwards move, if Meyer’s 
