222 ANATOMY OF THE KNEE-JOINT. 



femoral condyle ; and involve, in addition to the completion 

 and commencement of flexion and extension respectively, a 

 movement of rotation of the tibia and consequently of the 

 leg and foot inwards in the former, and outwards in the latter. 

 These remarkable movements of rotation inwards and out- 

 wards, inseparable from the commencement of flexion and the 

 completion of extension, take place round the axis of the 

 ideal cone already alluded to. This axis Meyer denominates 

 the oblique axis of the knee-joint. 



These movements of rotation, combined with flexion and 

 extension, must be carefully distinguished from those of which 

 the joint is capable when considerably flexed. The latter, 

 with which anatomists are already familiar, take place, in 

 general terms, round a prolongation of the axis of the tibia. 

 This axis Meyer denominates the rotation-axis of the knee- 

 joint. 



The most remarkable ligament concerned in the move- 

 ments round the oblique axis of the joint is the external cru- 

 cial, which becomes tightened in extension, as the movement 

 round the oblique curvature of the inner condyle proceeds, 

 and thus acts, from its obliquity, in a direction from below, up- 

 wards, backwards, and outwards, so as to guide the rotation 

 of the tibia outwards. 



The discovery of the oblique axis of the knee-joint has 

 enabled . Meyer to determine with greater precision the action 

 of certain muscles of the thigh. The use of the peculiar mode 

 of insertion, hitherto unexplained, of the sartorius, gracilis, 

 and semitendinosus, becomes- evident. Their tendons, passing 

 down behind the inner side of the knee, curve forwards and 

 outwards on the tibia ; so that these muscles effect that 

 rotation inwards which is a necessary accompaniment of the 

 commencement of flexion. These muscles produce this 

 rotation directly that is, by an adaptation of their tendons 

 to the purpose ; but, according to Meyer, the proper flexors 



