THE TIBIA 103 



The faint transverse ridges divide the articular surface 

 into an upper two-sixths, a middle three-sixths, and a lower 

 one-sixth. In usual extension the lower one-sixth is in contact 

 with the femur, in mid-flexion the middle three-sixths, and 

 in extreme flexion the upper two-sixths; also in extreme flexion 

 the thin marginal facet is the part in contact with the inner 

 condyle. Below the articular surface is a rough triangular 

 area; the ligamentum patellae springs from the apex. 



Place the patella upon a plane surface, its apex away from 

 you and its anterior surface up. It will tip to the side to which 

 it belongs. 



THE BONES OF THE LEG 



The Tibia 



The tibia (flute), or shin bone, is the inner and anterior of 

 the two bones of the leg, and transmits the weight of the trunk 

 to the foot. It articulates with the femur, fibula, and astragalus ; 

 has a shaft and two extremities. 



The superior extremity, or head, is thick and broad trans- 

 versely. It forms on each a tuber osity. These are continuous 

 in front, but separated behind by a notch, the popliteal. 



On the upper aspect of each tuberosity is a concave articular 

 surface for the condyles of the femur. The internal tuberosity 

 is larger than the external, and marked posteriorly and internally 

 close below the articular surface by a horizontal groove for 

 the semimembranosus. 



The condylar surface is oval, more hollowed than the external, 

 and longer. 



The external tuberosity at the junction of the anterior and 

 outer surfaces forms a prominent tubercle for the insertion of 

 the iliotibial band; below this are often attached a few fibers 

 of the extensor longus digitorum and of the biceps. At the 

 posterior and under part is a flat articular surface for the 

 fibula, looking down, out, and back. The external condylar 

 surface is nearly circular, concave from side to side, and more 

 or less convex from before backward; it is prolonged a little 

 posteriorly where the popliteus glides. The periphery of each 

 articular surface is flattened for the semilunar fibrocartilage. 



