The Lower Extremity and Pelvis 



157 



Tibialis posticus lies between the postero- internal and interosseous borders : between the 

 postero-external and the anterior edges is the external surface that gives origin to 

 the peroneal muscles. 



The lower end has a triangular subcutaneous surface externally, ending in the 

 (outer) nuillcolns below, a longer projection than the malleolus of the tibia : this 

 has a triangular articular face 

 internally for the astragalus, and 

 a deep digital fossa behind this for 

 the posterior part of the external 

 lateral ligament : above the 

 articular surface is a small facet 

 for the tibia, and above this 

 again is a rough ligamentous area 

 for the lower interosseous ligament, 

 from the upper and front part of 

 which the interosseous border is 

 continued up on the shaft. 



The external or peroneal sur- 

 face, traced down, leads to a broad 

 groove on the back of the lower 

 end, showing where the Peronei 

 pass behind the ankle : Peroneus 

 longus arises from the upper half 

 of the outer surface, and P. brevis 

 from the lower half. 



The two bones are held together 

 by an interosseous membrane, of 

 which the fibres are mainly directed 

 downwards and outwards and are 

 very short below : here it is con- 

 tinuous with the interosseous liga- 

 ment, consisting of several groups 

 of fibres with fatty tissue interven- 

 ing, which causes the roughened 

 areas into which the interosseous 

 borders are continued on the lower 

 parts of both bones. 



There are also upper and lower 

 tibio-fibular ligaments on the upper 



oufet- aspect. 



FIG. 129. Right fibula. Inner and outer views. Th& 



and lower joints : these again can bone as a whole is usually slightly concave forward, 



and this, with the recognition of parts at the lower 

 end, will enable the student to place the bone on its 

 proper side. 



be divided into anterior and poste- 

 rior, and in all there is the same 

 general direction, downwards and 



outwards. The lower ligaments are the strongest, and the upper anterior is stronger 

 than the posterior. The upper joint has a weak capsule above, often perforated for 

 a connection between its cavity and the bursa round Popliteus tendon : it has an 

 indefinite oblique band below, directed downwards and inwards. The lower joint 

 cavity is only a very short prolongation of synovial membrane of the ankle, and there is 

 frequently no articular cartilage on the contiguous surfaces of the bones : the lower 



