206 TIBIA. 



condyle of the thigh bone moves. The circumference of these 

 cavities is rough and unequal, for the firm connexion of the 

 ligaments of the joint. Immediately below the edge, at its 

 back part, two rough flattened protuberances stand out ; into 

 the internal, the tendon of the semimembranosus muscle is 

 inserted ; and a part of the cross ligament is fixed to the exter- 

 nal. On the outside of this last tubercle, a smooth slightly 

 hollowed surface is formed by the action of the popliteus 

 muscle. 



Before the forepart of the upper end of the tibia, a large 

 rough protuberance rises, to which the strong tendinous liga- 

 ment of the patella is fixed. On the internal side of this, there 

 is a broad scabrous slightly hollowed surface, to which the 

 internal long ligament of the joint, the aponeurosis of the vastus 

 internus, and the tendons of the semitendinous, gracilis, and 

 sartorius, are fixed. Below the external edge of the upper 

 end of the tibia, there is a flat circular surface, covered in a 

 recent subject with cartilage, for the articulation of the fibula. 

 The body of the tibia is triangular. The anterior angle is very 

 sharp, and is commonly called the spine or shin. This ridge is 

 not straight ; but turns first inwards, then outwards, and lastly 

 inwards again. The plane internal side is smooth and equal, 

 being little subjected to the actions of muscle ; but the external 

 side is hollowed above by the tibialis anticus, and below by 

 the extensor digitorum longus and extensor pollicis longus. 

 The two angles behind these sides are rounded by the action 

 of the muscles ; the posterior side comprehended between them 

 is not so broad as those already mentioned, but is more oblique 

 and flattened by the action of the tibialis posticus and flexor 

 digitorum longus. A little above the middle of the bone, the 

 internal angle terminates, and the bone is made round by 

 the pressure of the musculus soleus. Near to this, the 

 passage of the medullary vessels is seen slanting obliquely 

 downwards. 



The lower end of the tibia is hollowed, with a small protu- 

 berance in the middle. The internal side of this cavity, which 

 is smooth, and in a recent subject is covered with cartilage, is 



