398 



HUMAN ANATOMY. 



part by the interosseous membrane. The antero-external surface presents the fol- 

 lowing features: (i; a large surface of the tibia, looking outward as far as the 

 lower third and then forward ; (2) the interosseous membrane ; (3) a narrow' sur- 

 face of the fibula, bounding externally the fossa of the front of the leg, shallow 

 above, deep and narrow below ; (4) the antero-external border of the fibula, split- 

 ting below to enclose the subcutaneous surface above the outer malleolus ; (5) the 

 grooved surface of the libula occupied by the peronei. 



The posterior surface presents, continuing in the same course : ( i ) the posterior 

 surface of the fibula, looking backward above, inward below ; (2J the postero-in- 

 ternal border, ending in the interosseous ridge ; in the upper two-thirds this over- 

 hangs a deep hollow ; (3) the internal surface, which ends below with the preceding 

 border; (4) the interosseous membrane; (5) the posterior surface of the tibia. 

 The interosseous membrane is at the bottom of a much deeper gutter than in front, 

 which also becomes very narrow below. 



The outward twist of the ankle has been mentioned, and it has been shown that 

 this depends on the twist of the tibia. It is to be noticed that while the antero- 

 external, the postero-external, and the postero-internal borders of the fibula run as if 



Anterior border 



Fig. 413. 



B 



Internal 

 border 



Anterior border 



Oblique line 

 Postero-int. border' 



Internal border 



Antero-ext. border 



Postero-int. border^ 

 Postero-ext. border 



Anterior border 



Anteroext. border 

 Internal border 

 Postero-ext. border 



Antero-ext 

 border 



Postero-ext. border 



Sections across the bones of right leg, showing their relations at different levels ; seen from above. A, near head of 



fibula ; B, near the middle ; C, a little above the ankle. 



the lower end of that bone had been twisted outward, the same is not true of the 

 borders and surfaces of the tibia. On the contrary, the crest, with the surface on 

 each side of it, slants in the lower half of the leg downward and inward. It is as 

 if these borders of both bones had been twisted away from the median line of the 

 leg, one to each side, and that the interosseous ridge had stayed straight. There 

 seems to be no relation between the degree of forward bend of the neck of the 

 femur and the outward twist of the socket of the ankle. Probably both have an 

 influence on the direction of the foot, but it depends chiefly on the latter. It is un- 

 warranted, therefore, to expect all children to turn out the toes alike. The whole 

 of the front and sides of the head of the tibia is easily felt, but it is thickly covered 

 behind. The top of the tuberosities is clear on either side, and in front the whole 

 of the tubercle can be explored when the'tendon is relaxed. The head of the fibula 

 is distinct far back on the outer side. Descending the leg, it is easy to follow the 

 sharp crest of the tibia into the lower third, and the internal subcutaneous surface 

 down to the malleolus. The external surface, where it becomes anterior above the 

 ankle, is plain in spite of the tendons crossing it. The shaft of the fibula is so 

 covered with muscles that litde more than its general position is to be made out 

 above the triangular subcutaneous surface over the outer malleolus, which latter is 

 also easily explored. The relations of the malleoli are considered with the foot 

 (page 449). 



• THE PATELLA. 



The knee-pan, the largest sesamoid bone, is triangular or shield-shaped. The 

 anterior surface is covered by the tendinous fibres of the quadriceps, which re- 

 place the periosteum and mark the surface with longitudinal lines. Jagged spines 

 from the ossification of the tendon are often found at the top. The transverse 



' In the transverse sections (Fig. 413) this surface is exceptionally small. 



