82 



The os cuboides receives the superincumbent weight from the astra- 

 galus and naviculare, and transmits it to the os calcis, and to the three 

 outer metatarsal bones. 



446. The os naviculare. 



The naviculare is an irregular, thick, oval plate of bone, concave 

 towards the astragalus, convex next the metatarsus. Its thickest part is 

 towards the upper and outer end, where the articular surface for the 

 astragalus is slightly convex ; the rest of that surface which extends to 

 the tibial and lower border of the naviculare is concave ; the upper and 

 posterior border of the bone presents accordingly a sigmoid curve. The 

 thickest part of the margin of the bone, which is above the convex articu- 

 lation with the astragalus, is rough and flattened : the angle between 

 this and the outer margin is formed by a thick tuberosity, only a small 

 part of the anterior convex surface is modified for articular union, and 

 this part presents two distinct surfaces for two cuneiform bones : of 

 these articulations the outer is more than double the extent of the inner 

 one, and one forms an oval of one inch and a half by one inch in dia- 

 meter ; it is gently convex and situated towards the lower half of the 

 fibular part of the anterior surface : the outer surface is about ten lines 

 by seven lines in extent, situated, with its long axis transversely, close 

 to the inner margin of the line, nearer the lower than the upper mar- 

 gin, and separated by an uneven, non-articular tract of nearly half an 

 inch in extent from the external cuneiform surface. 



44/ The external os cuneiforme. 



A vacant interspace in the skeleton divides the cuboid from the ex- 

 ternal cuneiform bone, which has the usual triangular form, with the base 

 shorter than the sides : it presents only two articular surfaces, a posterior 

 one, slightly concave, for the naviculare, and an anterior one, in a less 

 degree convex, for the oblique base of the middle metatarsal ; the outer 

 angle of the base of the anterior surface is more produced than that of 

 the posterior surface. The external cuneiform diminishes in antero- 

 posterior thickness from the base towards the apex, which is rounded off". 

 The three margins of the bone are flat or slightly convex, rough and 



