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tuberosities, one above, which supports the inner extremity of the. astra- 

 galar articulation ; another below, forming the internal and anterior 

 angle of the inferior subconcave surface ; the third in front, constituting 

 the anterior prolongation of that surface. There is but one articular 

 surface in the os calcis of the Mylodon, which occupies the whole of 

 the narrow superior facet, and bends down over part of the anterior sur- 

 face : the upper division of the articular surface supports the astragalus ; 

 it is slightly concave transversely, convex from behind forwards at its 

 middle part : its breadth is not quite equal to the surface of the astra- 

 galus which plays upon it, and it is evident that a certain freedom of 

 lateral motion was allowed between these two bones. The anterior 

 deflected division of this long and narrow articular surface is equal to 

 one-fourth of its entire extent ; it is slightly concave, and adapted to 

 the os cuboides. 

 445. The os cuboides 



The os cuboides has the form rather of a thick and short wedge, the 

 base of which is formed by the rough flat subquadrate surface, which 

 appears at the upper and outer part of the tarsus ; the outer and anterior 

 margin of this surface is developed into a rough eminence. On the 

 outer side of the cuboides, there is a slightly convex surface for the 

 calcaneum, the whole of the back part is excavated to receive the 

 astragalar tuberosity ; a narrow vertical strip of articular surface on 

 the inner surface joins the naviculare, and these three facets are con- 

 tinuous with each other. At the fore and upper part of the inner 

 side of the cuboides, there is a small surface which touches the base of 

 the third metacarpus, this is separated from the navicular strip by a 

 rough depression bounding the interspace between the cuboid and ad- 

 joining cuneiform bone ; the anterior surface of the cuboides supports a 

 very large articulation divided by a vertical narrow groove into two parts, 

 for the two outer metatarsal bones. The under part of the cuboides is 

 excavated by a rough depression, bounded anteriorly by a rugged protu- 

 berance. Although the cuboides articulates with six distinct bones, it 

 has only two distinct smooth articular tracts, that for the middle meta- 

 tarsal being continuous with the large outer metatarsal surface. 



M 



