70 



oblong tuberosity on each side. On the fore part of the bone (ib. fig. 3) is the articular 

 surface, divided into the narrow oblong tract (cm), with two slight convexities, for the 

 mesocuneiforme (ib. fig. l,f), and into the almost flat triangular tract (fig. 3, ci) for the 

 ectocuneiforme (fig. 1, e). The latter surface (fig. 3, ci) is divided by a very narrow non- 

 articular tract from the cuboidal surface (fig. 3, cb"). The inner (tibial) part of the 

 anterior surface is non-articular, and extends beyond the mesocuneiform articulation to 

 where the entocuneiforme would have been, had that bone existed in the tarsus of the 

 Megatherium. 



The mesocuneiforme* (Plates XXV. & XXVI. fig. 1, /) is a laterally compressed 

 reniform bone, with a thick rough convex inferior border: the inner (tibial) surface 

 (Plate XXV. fig. 1, f) is irregular and flattened: the similarly modified outer (fibular) 

 surface (Plate XXV. fig. 2, f) is varied by a flat elliptic articular facet (Hi) near its 

 upper part, for a similar surface on the side of the metatarsal of the 'digitus medius.' 

 The back part of the bone is chiefly occupied by the narrow surface for the naviculare. 

 The fore part of the bone is obtuse and rough. Not a vestige of the toe (digitus secundus), 

 usually supported by the mesocuneiforme, is developed in the Megatherium. 



The ectocuneiforme f (Plates XXV. & XXVI. fig. 1, e) presents the normal wedge-like 

 figure of the tarsal cuneiform bones. It is flattened from before backward ; with its 

 thick base (e) rough and convex. The posterior surface presents the almost flat, slightly 

 concave articular surface for the naviculare. The outer border or surface is rough and 

 tuberous; the inner one less rough and flat. The anterior convex facet (Plate XXV. 

 fig. 2, Hi) for the base of the metacarpal does not extend to the upper or under borders 

 of the bone. The articulation with the contiguous cuneiforme, as with the cuboides, is 

 by syndesmosis. 



The cuboides (Plate XXVI. fig. 1, d) presents an articular surface divided into three 

 facets on its upper, or tibial, and back part ; the anterior and smallest facet is for the 

 naviculare (c), the middle and largest for the astragalus (a), and the posterior for the 

 calcaneum (ib) : the latter surface is at almost a right angle with the astragalar one, and 

 looks backward. On the under, or fibular, and fore part of the bone is the articular 

 surface for the two outer metatarsals ; that for the fourth toe (Plate XXV. fig. 2, iv) 

 being concave transversely and slightly convex lengthwise ; that for the fifth toe (ib. v) 

 being uniformly but very slightly convex. 



A broad non-articular surface, rough and with two oblique low ridges on the upper 

 and outer part of the bone, divides the back from the front articular surface ; a narrower 

 non-articular tract, but produced into a strong obtuse ridge, divides the same surfaces 

 on the inner or under side of the bone. The fore part of the bone is produced into an 

 angular process (Plate XXV. fig. 2, p), which forms the inner part of the articular 

 channel for the fourth metatarsal. The under part of the bone is impressed by the 

 broad tendinal groove continued from that which impresses the outer part of the calca- 

 neum. 



• ' Os cuneiforme medium ' of Sosmmerbixg. f ' Os cuneiforme externum,' ib. 



