MOVEMENTS OF KNEE AND PATELLA. 641 



Rotation. A half bent state of the knee is necessary for this movement, 

 for the purpose of relaxing the anterior crucial and the external ligaments ; 

 and the foot must be free. Then, the tibia with its fibre-cartilages rotates 

 around a vertical axis, the great toe being turned in and out. 



During rotation in the inner articular surface of the tibia touches the 

 condyle of *the femur and moves backwards; and the outer articular sur- 

 face, separated by a slight interval from the thigh bone, passes forwards. 



Both lateral ligaments are loose ; but the anterior crucial is gradually 

 tightened, and stops finally the motion. 



In rotation out the opposite movement of the tibia takes place the in- 

 ner articular surface being directed forwards, and the outer backwards. 



The internal lateral ligament controls the movement by its fibres being 

 made tense. The crucials have not any influence on the motion (p. 637). 



Movement of the patella. When the knee passes from flexion to exten- 

 sion the patella crosses it obliquely from the outer to the inner side, touch- 

 ing in succession different parts of the femoral articular surfaces. 



In complete flexion the knee-pan lies on the outer side of the joint 

 below the femur, where it is scarcely perceptible, and is fixed in its situa- 

 tion. It touches the semilunar surface on the inner condyle by its per- 

 pendicular facet, and the under part of the outer condyle by the upper and 

 outer mark on its square surface. 



When the joint is passing from flexion to extension, the upper pair of 

 impressions on the square surface of the patella, and the lower pair rests 

 successively on the pulley-surface of the femur. 



In complete extension, the patella is situate at the upper and inner 

 part of the knee-joint, where it is very prominent, with its apex and the 

 ligament of the patella directed down and out to the tibia. For the 

 most part the knee-pan articular surface is raised above the trochlea 

 of the femur, which it touches only at the upper edge by its lower trans- 

 verse facet. 



PERONEO-TIBIAL ARTICULATIONS. The tibia and fibula are united by 

 ligamentous bands at the extremities, where they touch ; and by an inter- 

 osseous ligament between the shafts of the bones. 



Dissection. The muscles are to be taken away from the front and back 

 of the interosseous ligament ; and the loose tissue is to be removed from a 

 small band in front of, and behind the upper and lower ends of the tibia 

 and fibula. 



The UPPER ARTICULATION has very small movement, and the structures 

 between the ends of the bones are two small bands, anterior and posterior. 



The anterior ligament extends over the joint from the outer tuberosity 

 of the tibia to the head of the fibula. The posterior ligament, thinner 

 than the anterior, is attached to the bones behind the joint : it is covered 

 by the tendon of the popliteus muscle and a prolongation of the synovial 

 membrane of the knee-joint. 



The articular surfaces are covered with cartilage : and a synovial mem- 

 brane lining the articulation projects backwards so as to touch that of the 

 knee-joint. 



The LOWER ARTICULATION possesses an anterior and a posterior band, 

 together with an inferior ligament between the ends of the bones. 



The anterior ligament reaches obliquely from the lower end of the tibia 

 to the fibula ; and the posterior has attachments behind the articulation 

 similar to those of the band in front. 



The inferior ligament closes the space between the contiguous ends of 

 41 



