THE TIBIO-FIBULAR UNION 



263 



ligamentum patellae and front of the capsule. Extension is checked by both the 

 crucial ligaments and the lateral ligaments (figs. 250, A, B, and 251). 



In flexion the ligamentum patellae and anterior portion of the capsule are on 

 the stretch; so also is the posterior crucial in extreme flexion, though it is not quite 

 tight in the semiflexed state of the joint. All the other ligaments are relaxed (fig. 

 250, C, D), although the relaxation of the anterior crucial ligament is slight in 

 extreme flexion (fig. 252). Flexion is only checked during life by the contact of 

 the soft parts, i.e. the calf with the back of the thigh. 



Fig. 252. — Ckucial Ligaments in Flexion. 



Posterior crucial 



Anterior crucial 



Internal semilunar 

 cartilage 

 TraBsverse ligament 



Slip from external cartilage to femur 

 Extsrnal semilunar cartilage 



Coronary ligament 



Antero-superior tibio-flbular ligament 



Inward rotation is checked by the anterior crucial ligament; the lateral liga- 

 ments being loose. 



Outw'ard rotation is checked by the lateral ligaments; the crucial ligaments have 

 no controlling effect on it, as they are untwisted by it. 



Sliding movements are checked by the crucials and lateral ligaments — sliding 

 forwards especialh^ by the anterior, and sliding backwards by the posterior crucial. 



3. THE TIBIO-FIBULAR UNION 



The fibula is connected with the tibia throughout its length by an interosseous 

 membrane, and at the upper and lower extremities by means of two joints. Very 

 little movement is permitted between the two bones. 



(a) The superior tibio-fibular joint. 

 (6) The middle tibio-fibular union, 

 (c) The inferior tibio-fibular joint. 



(«) The Superior Tibio-fibular Joint 

 Class, — Diarthrosis. Subdivision. — Arthrodia. 



The superior tibio-fiV)ular joint is about a quarter of an inch (6 mm.) below, and 

 quite distinct from, the knee at its upper and anterior part; but at its posterior and 



