ANATOMY OF THE KNEE-JOINT. 221 



its concavity directed backwards, outwards, and do^\^lwards. 

 The two posterior thirds of the inner condyle pass backwards 

 parallel to, and have the same general form and extent as, the 

 entire outer condyle of the bone. The curved portion or 

 anterior third of the usually so-called inner condyle may 

 therefore be conceived as a part intercalated between the 

 patellar trochlea and the i)roper inner condyle. 



According to Meyer, the mechanical advantages which 

 result from the peculiar antero-posterior curvatures of the 

 femoral condyles, which the l)rf)thers "SVeber concluded, from 

 their admeasurements, to bo spirals, may be with greater 

 simplicity assumed to consist, as his own ailmeasurements 

 suggest, each of two cu'cular segments, the posterior of 120°, 

 the anterior of 40°, the radius of the former being to that of 

 the latter as 5 to 0. The horizontal curvature at the fore-part 

 of the imier condyle, or, more precisely, the oblique cur\ature, 

 may, as Meyer states, be conceived as a segment of G0° of the 

 margin of the base of a cone, the axis of wliich is directed at 

 an angle of 45° downwards, outwards, and backwards, in front 

 of the spine of the tibia, so that its apex is situated in the 

 external condyle of that bone. 



In flexion and extension, therefore, of the knee-joint, as 

 long as these movements are confined to the outer condyle, 

 and the two posterior thirds of the inner condyle of the femur 

 with the condyles of the tibia, they take place roimd two 

 transverse axes, which pass respectively through the centres 

 of the posterior antero-posterior circular curvatures of tlie 

 femoral condyles, and the centres of the anterior. To simplify 

 the conception, however, of this part of the arrangement, 

 Meyer assumes as sufficiently accurate a single transverse 

 axis. 



In the first third of flexion, and in the latter third of ex- 

 tension, the movements of the fomur and tibia take place 

 round the obli(pie curvature or anterior third of the internal 



