THE TIBIA. 



Ill 



are oval in form, the external being wider transversely, and the 

 internal longer from before backwards. Between them is an irreg- 

 ular interval, depressed in front and behind, where it gives attach- 



Fig. 99. Fig. 99. — Right Tibia from before. (A. T.) i 



1, shaft, and shin or anterior border ; 2, inner tube- 

 rosity ; 3, outer tuberosity ; 4, inner, and 5, outer, 

 condylar articular surface ; 6, crucial spine, witli fossa 

 at its root in front ; 7, anterior tuberosity ; 8, lower 

 articular surface for astragalus ; 9, malleolus interuus. 



ment to the crucial ligaments and semilunar 

 cartilages of the knee joint, and elevated 

 in the middle, where is formed thejjpincl' 

 The summit of the spine presents two pro- 

 minent tubercles, formed by the prolonga- 

 tion upwards on its sides of the margins 

 of the condylar portions ; the outer being 

 turned slightly forwards, and the inner 

 slightly backwards. On the sides of the 

 upper extremity of the bone are two rounded 

 eminences, the external and inierfud iuher- 

 osities ; the outer one of these, somewhat 

 smaller than the other, is marked posteriorly 

 by a flat surface which articulates with the 

 fibula, while the inner presents a groove for 

 the insertion of the semi-membranosus mus- 

 cle. Lower down, in front, is situated the 

 anterior tuherosity or tuhercJe, rough inferiorly, 

 where it gives attachment to the ligamentum 

 jjatellfe, and smooth above, where it is 

 covered by a synovial bursa. 



The sJiaft of the tibia is three-sided, and 

 diminishes in size as it descends for about 

 two-thirds of its length, but increases some- 

 what towards its lower extremity. The 

 internal surface is convex and subcutaneous, 

 except at the upper part where it is crossed 

 by the tendons of the sartorius, gracilis, and 

 semitendinosus muscles. It is separated from 

 the external surface by a sharp subcu- 

 taneous, shghtly sinuous crest, the shin ridge, 

 which descends from the anterior tuberosity, 

 and is smoothed away in the inferior third 

 of the bone. The external stnface is slightly 

 hollowed in the larger part of its extent, 

 where it gives origin to the tibialis anticus muscle ; but beneath the 

 point where the crest disappears it turns forwards, becomes convex, and 

 is covered by the extensor tendons. The ^^osferior surface is traversed 

 obliquely in its upper third by the popliteal line — a rough mark which 

 extends upwards and outwards to the external tuberosity, giving attach- 

 ment to the soleus muscle, and separating a triangular area, in which 

 the popliteus muscle lies, from the space below, which gives origin to the 

 flexor longus digitorum and tibialis posticus. The posterior surface is 



