PELVIC LIMBS 713 



facet for the fibula, and passes obliquely downward and forward to 

 occupy the middle line of the outer aspect of the bone in its lower 

 fourth, and to end at the apex of the triangular articular facet for the 

 lower extremity of the fibula. The border is sharp, and defines the 

 outer edge of the tibial area of origin of the flexor longus hallucis 

 muscle. 



The internal border (Fig. 547) may be easily mistaken, inasmuch 

 as there is an apparent internal border which limits the inner aspect 

 of the bone, but is not the true internal border, which is the point 

 of division of muscular and aponeurotic attachment. This internal 

 border lies in front of the apparent border, and begins above in the 

 roughened line for the insertion of the internal lateral ligament ; it 

 then curves slightly forward, and at the middle of the bone lies exactly 

 in the median line of the inner aspect. From this point it curves 

 backward, and at the lower fourth runs along the posterior edge of 

 this aspect of the bone. The upper end of the internal border affords 

 insertion for the internal lateral ligament. The aponeurosis of the 

 gracilis and semitendinosus is attached from about the middle down 

 to the lower end. In the upper fourth of the bone the border marks 

 the inner edge of the area of insertion of the popliteus muscle, in the 

 middle fourth that of the flexor longus digitorum, and for a short 

 distance in the upper part of the lower fourth that of the flexor longus 

 hallucis. 



The posterior surface of the shaft (Fig. 546) is defined by the 

 external and internal borders, and is wider above than below. Its 

 external edge is slightly sinuate, and visible for its entire length when 

 the bone is viewed from behind ; but the internal border is on the 

 internal aspect of the bone except near the lower extremity. The 

 posterior surface is sharply separated from the upper extremity by 

 the prominent posterior border of the head ; it is continuous below 

 with the posterior surface of the lower extremity. It is divided by a 

 longitudinal ridge namely, the apparent internal border into (1) a 

 very narrow internal part and (2) a broad external part. The greater 

 portion of the internal .part faces inward, and all of the external part 

 faces directly backward. The ridge begins above, just on the inside of 

 the popliteal or intercondyloid notch, and runs obliquely through the 

 upper fourth nearly to the internal border, where it divides into two 

 branches, whereof one is continued to meet the internal border at a 



