514 THE CURVATURES OF THE ARTICULAR SURFACES, ETC. 



joint differ from those in the elbow and ankle in their axes 

 being nearly perpendicular to the horizontal plane of the 

 joint, that of the anterior being directed with its vertex 

 upwards and slightly backwards and outwards ; that of the 

 posterior upwards and slightly forwards and inwards. The 

 shallow transverse curvatures of the rolling areas of the male 

 elements, and the wa'\'y convex form of the corresponding 

 curvatures of the female elements, would appear to render 

 lateral and circimiductory movements of the knee-joint 

 possible. It will be found, however, that throughout the 

 whole extent of its double helicoid movements, it only permits 

 of eversion and inversion of the toes at the stage beyond semi- 

 flexion ; these movements, due to the action of the biceps and 

 semi-membranous being again excluded when the joint is 

 flexed home. 



The hip-joint, from the ball and socket form assumed by 

 its combined anterior and posterior screw combinations, is not 

 only capable of pursuing its fundamental double helicoid 

 path, but also of performing the so-called adduction, abduc- 

 tion, and circumduction movements in all j)arts of its course, 

 but more particularly towards the close of flexion. 



