THE TIBIO-FIBULAR ARTICULATIONS. 189 



posterior crucial ligament is in part relaxed ; in flexion, the posterior crucial ligament only is 

 tightened, the others being' relaxed. Over-extension is prevented, not only by the tension of 

 the ligaments, but also by the anterior portions of the semilunar nbro-cartilages being pressed 

 into the grooves of the femoral articular surface, and the anterior margin of the intercondylar 

 fossa meeting the lower end of the anterior crucial ligament. In the last stage of the move- 

 ment of extension the inner part of the outer groove of the femur plays over a special facet 

 of the tibia in front of the outer tubercle of the spine (fig. 210). In extension of the joint 

 no rotation of the leg is possible ; in the flexed condition a considerable amount is allowed. 

 Rotation out is checked by the internal lateral ligament, in by the anterior crucial ligament : 

 the whole range of movement, when the knee is bent to a right angle, is on an average about 

 40 ; but it varies much in different individuals. The semilunar fibre-cartilages^ being loosely 

 attached to the head of the tibia, move forwards in extension and backwards in flexion of 

 the joint ; and farther, as the condyles rolling upon the tibia present successively to the 

 condylar surfaces of that bone portions having different curvatures, each cartilage, like a 

 moveable wedge, is contracted round the condyle during flexion of the joint and expanded 

 during extension. The mass of fat below the patella serves to fill up the space between the 

 ligamentum patellae and the bones, and adapts itself to the varying form of this interval 

 during the movements of the joint, the alar ligaments projecting upwards into the angle 

 between the lower part of the patellar surface and the femur. 



In the erect attitude, the knee-joint, like the hip, is maintained in the fully extended posi- 

 tion in great measure without muscular effort ; but there is some difference of opinion as to the 

 manner in which this is effected. According to the one view, which is supported by Humphry 

 and Langer, the line of gravity of the body falls in front of the axis of movement of the knee- 

 joint, and the tendency is thus to over-extension, which is resisted by nearly all the ligaments of 

 the articulation. On the other hand H. Meyer holds that the line of gravity falls slightly behind 

 the axis of movement, and that the stability of the knee depends mainly upon the association of 

 rotation with the beginning of flexion ; for, while the tibia is fixed by its connection with the 

 foot, the femur is prevented from rotating outwards by the ilio-femoral ligament, which in 

 its turn is kept tense by the weight of the body acting on the hip-joint. Rotation between 

 the tibia and femur being thus impossible, flexion cannot take place, and the knee-joint is 

 fixed until by a slight bending at the hip-joint the ilio-femoral ligament is relaxed. Addi- 

 tional support is also given to the knee-joint by the tension of the ilio-tibial band of the 

 fascia lata (pp. 242 and 249). (H. Meyer, Miiller's Archiv, 1853 ; Goodsir, " Anatomical 

 Memoirs," ii, 220. 231 ; Langer, Sitzungsber. d. Acad. der Wissensch. Wien, 1858, and " Lehrb. 

 d. Anat." ; Humphry, >( A Treatise on the Human Skeleton ; " Henke, Zeitschr. fiir rat. Med., 

 viii, 1859 ; R. Bruce Young, On the grooves of the femur and locking of the knee-joint, in 

 ' ; Memoirs and Memoranda in Anatomy," 1889.) 



THE TIBIO-FIBULA .1 ARTICULATIONS. 



The tibia and fibula form articulations at their upper and lower extremities, 

 and their shafts are united by an interosseous membrane. 



Upper tibio-fibular 

 articulation. The supe- 



... I A ^S~*-" /ANT.INF.TIBrFIB.LICT 



nor extremities or the 

 bones present two flattened 

 oval articular surfaces, re- 

 tained in close contact by 

 thin anterior and posterior 

 superior tibio-fibular liga- 



i-l,1 1'1 GROOVE OF' ^*^S^^^^Z^S&F Z **]~~~ \ GROOVE OF PERONE 



ments, both of which pass 



downwards and outwards 



from the external tuberosity 



of the tibia to the head of 



the fibula. The synovial Fig. 216. INFERIOR EXTREMITIES OF THE LEFT TIBIA AND 



cavity of this ioint not un- FIBULA, FROM BELOW, SHOWING THE UNITING LIGAMENTS ANI> 



* THE FORMATION OF THE SOCKET OF THE ANKLE-JOINT. 



frequently communicates (Drawn by T w R Lawrence.) 



posteriorly with that of the 



knee. 



The interosseous membrane or ligament, which connects the shafts of the 

 tibia and fibula, passes between the external border of the tibia and the interosseous 



