720 



MAMMALIAN ANATOMY 



of the groove for the flexor longus hallucis on the lower margin of the 

 posterior surface. 



Of the two facets thus separated, the inner is twice as long as it is 

 wide, concave in both directions, and faces almost directly downward. 

 Its long diameter is directed from in front backward and inward, its 

 anterior margin is nearly straight, its posterior end and its inner and 

 outer margins are gently arcuate. 



The outer articular facet is wider than the inner, its long axis is 

 more oblique, and its posterior margin is longer. Its outer margin is 

 strongly arcuate, and meets the less arcuate inner margin in anterior 



FIG. 549. 



Head. 



Tubercle. 



Shaft. 



Lower Extremity. 

 PLAN OF THE DEVELOPMENT OF THE TIBIA BY FOUR CENTRES. 



and posterior angles. It is concave from before backward and less 

 concave from side to side, and faces as much outward as downward. 

 This surface articulates with the inner side of the outer convexity of 

 the trochlear surface of the astragalus. Inasmuch as the fibula is also 

 applied to the outer side of the astragalus and prevents dislocation of 

 the joint in that direction, this surface of the tibia, just mentioned, 

 does not clasp the outer convexity of the astragalus as the inner 

 surface clasps the inner convexity, where there is no additional bone 

 to prevent lateral dislocation. 



Nomenclature. The Latin word tibia was used for a wind in- 

 strument resembling the clarinet, and, as this instrument was made 



