640 DISSECTION OF THE LEG. 



In rotation the fibre-cartilages follow the tibia! movements, but the ex- 

 ternal is most displaced by the projecting outer condyle of the femur. 



The accessory bands in front and behind serve to retain in place the 

 least fixed external fibro-cartilage ; thus the anterior ligament keeps for- 

 wards the fore part of that cartilage in flexion, and the posterior secures 

 the back of the same from displacement in rotation. 



Articular surfaces of the bones. The end of the femur is marked by a 

 patellar and two tibia! surfaces. 



The patellar is placed in the middle line above the others ; it is hol- 

 lowed along the centre, with a slanting surface on each side, the outer 

 being the larger of the two. 



The surfaces for contact with the tibia, two in number, occupy the 

 ends of the condyles, and are separated from the patellar impression by an 

 oblique groove on each side. On the centre of each is a somewhat flat- 

 tened part, which is in contact with the tibia in standing ; and at the 

 posterior third is a more convex portion, which touches the tibia in rota- 

 tion. 



The inner condyle of the femur is curved at its anterior third, the con- 

 cavity being directed out : this has been named the "oblique curvature." 

 Close to the curved part is a semilunar facet, which touches the perpen- 

 dicular surface of the patella in extreme flexion. 



On the head of the tibia are two slight articular hollows, the inner being 

 the deeper and larger, which rise towards the middle of the bone, on the 

 points of the tibial spine. 



The joint-surface of the patella is marked by the following impressions. 

 Close to the inner edge is a narrow perpendicular facet, and along the 

 lower border is a similar transverse mark. Occupying the rest of the 

 bone is a squarish surface, which is subdivided by a vertical and a trans- 

 verse line into two pairs of marks upper and lower. (Goodsir, Edinb. 

 Med. Jour., 1855.) 



Movements of the joint. The chief movements of the knee are two in 

 number, bending and straightening, like the elbow ; but there is, in addi- 

 tion, rotation of the tibia when the joint is bent. 



Flexion and extension. Each of these movements may be divided into 

 stages for the purpose of particularizing changes in its direction. 



\i\flexion the tibia with its fibre-cartilages moves backwards round the 

 end of the femur ; and its extent is limited by the extensor muscle, and 

 by the meeting of the calf of the leg with the thigh. 



For the anterior third of the movement the tibia is directed down and 

 in along the oblique curve of the inner condyle, giving rise to rotation 

 inwards of that bone ; but for the posterior two-thirds, the tibia passes 

 straight back over the condyles. 



All the external ligaments are relaxed, except the anterior ; and both 

 crucials are put on the stretch towards the end of flexion. 



In extension the tibia is carried forwards until it comes into a straight 

 line with the femur, when the uniting ligaments prevent its farther 

 progress. 



In the hinder two-thirds of the movement the tibia has a straight 

 course over the condyles of the femur ; but in the anterior third the leg- 

 bone is directed up and out over the oblique curve of the inner condyle, 

 and is rotated out. 



All the external ligaments except the anterior are tightened, and the 

 crucial cords help to limit extreme extension. 



