115 



patch of smooth synovial surface is continued from the outer articular ca- 

 vity upon the hack part of this projection, for a post-tibial sesamoid bone.^The 

 under part of the process supports a flat elUptical articular surface *, not quite 

 parallel with the upper one, hut sloping from without inwards and downwards : 

 this is adapted to the head of the fibula, which thus underprops the projecting 

 bony platform, and supports, by the intervention of this and the semilunar car- 

 tilage, the outer condyle of the femur. 



The shaft of the tibia is continued directly downwards from the rest of the 

 circumference of the broad proximal end : it swells out anteriorly into irregular 

 rough convexities, forms a smoother border about the inner articular surface, 

 and falls in on every side to the lower third of the shaft, at the beginning of 

 which the bone presents its smallest circumference. The anterior surface, below 

 the proximal rough swellings, is flattened, and meets the posterior surface at a 

 concave edge externally ; the inner concave border of the shaft is thick and 

 rounded, A short rough ridge is continued from the middle of the anterior 

 proximal tuberosity obliquely downwards and inwards. Fine reticular risings 

 mark the smoother parts of the anterior surface. A broad but shallow groove 

 runs from the lower part of the outer concave edge downwards upon the anterior 

 surface of the expanded distal end of the bone. The outer malleolus projects as 

 a somewhat square-shaped protuberance. The opposite side of the distal end, or 

 the inner malleolus, forms a less prominent convex tuberosity. The posterior 

 surface of the tibia is smooth at the concavity beneath the overhanging fibular 

 articulation, and along the outer half of the posterior surface as far as the rugged 

 rising which overhangs the distal articular surface. The inner half of the back 

 part of the tibia presents a rougher surface : a rugged rising extends across its 

 upper part, a little below the convex boundary of the condyloid articular surface : 

 a thick rough ridge extends downwards to the middle of the internal concave 

 border of the shaft : a narrower ridge descends along the middle of the upper 

 half of the posterior surface and then divides, the inner branch extending obliquely 

 to the angle terminating the concavity of the inner margin of the shaft. Below 

 this ridge a wide and deep canal extends obliquely from above downwards and 

 inwards, its lower edge being about an inch above the distal articular margin : 

 this deep posterior excavation forms a well-marked character of the internal 



• Plate XX. fig. 2. c. 



p2 



