218 SKELETON. 



cave behind, and bulging at the sides. The flatness, in front, is 

 triangular, having its base upwards and the apex downwards, 

 the latter terminates in a well marked, broad, rough rising, 

 which is the tubercle of the tibia, and serves for the insertion 

 of the tendon of the patella. The concavity behind is made 

 by the popliteus muscle, and slopes from above obliquely in- 

 wards and downwards. The projection is great on the inter- 

 nal side of the upper extremity of the tibia, and at its posterior 

 part has a depression made by the insertion of the semi-mem- 

 branosus tendon. The external projection is thicker in front 

 than behind; at the latter point it has a small articular face, 

 looking downwards, for the head of the fibula. 



The inferior extremity of the tibia is much smaller than the 

 superior. It is terminated by a transverse quadrilateral cylin- 

 drical concavity, by which it articulates \vith the astragalus. 

 This concavity is narrower and deeper internally than external- 

 ly, and is traversed from before backwards by a low broad ridge. 

 It is bounded internally by the internal malleolus, a large pro- 

 cess of half an inch in length, the external side of which is a con- 

 tinuous surface with the cylindrical concavity, and forms part 

 of the joint. The other side of the malleolus is superficial, being 

 just beneath the skin. A shallow groove exists in its posterior 

 part, which transmits the tendons of the tibialis posticus and of 

 the flexor longus digitorum pedis. Inferiorly, the malleolus is 

 notched, or presents a depression, for the origin of the internal 

 lateral ligament, and just before the depression it is elongated 

 into a point. The lower end of the tibia presents, before and 

 behind, a slight swell, running transversely just above the arti- 

 cular surface. The posterior swell is occasionally slightly 

 marked by the tendon of the flexor longus pollicis pedis. 



Externally, the circumference of the lower end of the tibia 

 presents, longitudinally, a concavity which is in contact with 

 the lower end of the fibula. This concavity .terminates insen- 

 sibly above, but is deep below, where it is bounded before and 

 behind by an elevated point of bone, of which the posterior is 

 the highest. The concavity is placed nearly in the vertical line 

 of the little articular face for the fibula, on the head of the tibia; 

 and at its lower margin, there is frequently a small lunated sur- 



