456 APPENDIX. 



flexor muscle. From the peculiar spiral form of the articular surfaces, 

 when the knee-joint is fully extended the movement of flexion is 

 initiated by the action of the sartorius, gracilis, and semi-tendinosus, 

 which slightly rotate the leg and foot inwards. — (See vol. ii. p. 222.) 

 Similarly, when the joint is fully flexed, the movement of extension 

 is initiated by the action of the popliteus muscle, which brings the 

 joint into the horizontal position. 



