710 MAMMALIAN ANATOMY 



The external or fibular surface of the outer tuberosity (Fig. 544) 

 is narrow but well denned. Its upper border, which is at the same 

 time the outer border of the superior or proximal surface, is regularly 

 arched, and the anterior end extends lower than the posterior, termi- 

 nating in the side of the tibial tubercle. The lower border forms a 

 rounded posterior angle with the upper border, and passes forward and 

 upward to a point near its anterior third, where it is considerably 

 higher than at its origin. It here bends, nearly at a right angle, 

 sharply downward, and joins the superior border at the side of the 



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tubercle. The surface enclosed between these borders consists of two 

 parts, an oval posterior and a narrow anterior part. The long diame- 

 ter of the posterior part is directed upward and forward, and that 

 of the anterior part downward and forward. The surface is not ex- 

 actly vertical, but slopes from above outward as well as downward ; 

 at its middle is a nearly vertical groove for the tendon of the extensor 

 longus digitorum. The whole surface is rough for the attachment of 

 ligaments. 



The external surface of the tuberosity overhangs the external sur- 

 face of the shaft, and under it, near the posterior angle, is the oval 

 facet for the head of the fibula. 



The internal surface of the inner tuberosity (Fig. 547) differs from 

 the outer surface of the outer tuberosity in being practically in the 

 same plane as the internal surface of the shaft below, from which it 

 cannot be sharply distinguished. There are usually some traces of 

 the suture which separated the epiphysis of the head from the shaft, 

 and this suture may be considered the lower boundary of the surface. 

 The upper margin of the surface is curved, passing from behind for- 

 ward, at first upward, then forward, and then downward and forward, 

 and finally ending in front at the inner side of the tubercle. Its 

 posterior half is sharp and prominent ; the anterior half is rounded. 

 The surface may be said to be curved and to follow the superior border. 

 It is wider behind, where it faces downward and inward, than in front, 

 where it faces upward and inward. It is rough for the attachment of 

 ligaments, especially the capsular ligament of the knee-joint. A 

 shallow vertical groove not far from the posterior angle permits the 

 passage of the internal lateral ligament from the femur to the inner 

 side of the shaft. Just behind this groove is the area of insertion 

 of the semimembranosus muscle. 



