716 MAMMALIAN ANATOMY 



pies the outer aspect of the bone ; it then twists to the front and faces 

 forward and outward, until at the lower end it appears as an anterior 

 surface. Its upper part is nearly flat or slightly concave from before 

 backward, concave from above downward, and is overhung above by 

 the external surface of the upper extremity and in front by the 

 prominent everted anterior border or crest. In the angle thus formed 

 is the area of tibial origin of the tibialis anticus muscle. The lower 



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two-thirds of the surface are convex from side to side, and at first 

 convex and then somewhat concave from above downward. No muscle 

 arises from this surface, which is nearly covered by the muscles arising 

 higher up. 



The internal surface (Fig. 547) is wholly visible on the inner 

 aspect of the bone. It lies between the anterior and internal borders ; 

 there is no sharp line dividing it from the internal surface of the 

 upper extremity, and below it becomes the surface of the internal 

 malleolus. The internal surface is very wide above between the tibial 

 crest and the roughened line on the internal border which marks the 

 insertion of the internal lateral ligament. From this point it narrows 

 until at about the middle of the bone it is not quite one-fourth as wide 

 as it is above. It then gradually widens, and at the lower end is twice 

 as wide as at the middle. At its upper end it is concave from before 

 backward and from above downward ; lower down it is nearly flat from 

 before backward and convex from above downward ; below the middle 

 it is concave from above downward and convex from before backward. 

 In the upper part it faces forward as well as inward, and in the lower 

 part almost directly inward. There are no extensive areas of muscular 

 origin and insertion on the internal surface. The broad aponeurosis of 

 the sartorius is fastened on a curved line beginning above, near the 

 middle of the surface, and running forward to the most prominent 

 part of the tibial crest, where the upper fourth of the bone joins the 

 lower three-fourths. The aponeurosis of the semitendinosus and the 

 gracilis is inserted on a line which begins above where the sartorius 

 ends, and runs backward and downward to meet the internal border at 

 the middle of the bone. From this point the aponeurosis is blended 

 with the fascia covering the flexor longus digitorum and flexor longus 

 hallucis muscles, and continues down on the internal border nearly to 

 its end. 



The Lower Extremity is expanded laterally, principally on the 





