PEOrESSOE OWEN ON THE MEGATHEEIUM. 
817 
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 XL. 
fig. 2 , m) 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 XLI. 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 (t5) : 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 artiLlar 
surface for the two outer metatarsals; that for the fourth toe (Plate XL. fig. 2, w) 
being concave transversely and slightly convex lengthmse ; 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-aiticulai 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 XL. 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 calcaneum. 
The above-described composition of the tarsus of the Megatherium has been deduced 
from the study of three entire specimens of the bones of the hind foot ; and it demon- 
strates that the digits of that foot were but three in number, and that they answered 
to the ‘third, ‘fourth,’ and ‘fifth’ of the pentadactyle type. Not a rudiment of the 
‘ second exists, and every vestige of the first, together with the cuneiform bone support- 
ing it, is absent. There are no little bones missing on the inner side of the ‘ mesocunei- 
forme,’ as Dr. Paxdek conjectm-ed might be the case in the Madrid skeleton; and there 
is no ‘ os cuneiforme ’ for the hallux (‘ grand doit du pied ’), as Cuviee supposed. 
Ifetatarsies.— The metatarsal of the ‘ third ’ toe (Plates XL. & XLI. fig. 1, m 3 ) 
resembles rather an ‘ os cuneiforme,’ by reason of its extreme shortness, or fore-and-aft 
compression. Its upper non-articular surface is the broadest, and is rough and convex, 
like that of the ectocuneiforme. The proximal or posterior surface for that cuneiform 
bone is tiiangular and slightly concave (Plate XLI. fig. 3, ci) ; the bone is prolonged 
into a tuberous process beneath it, forming a lever of advantage for the insertion of a 
flexor tendon. On the inner side of the bone, at its upper part, is the small flat surface 
(cm) adapted to that on the mesocuneiforme ; on the outer side of the bone is a larger 
surface, partly convex, partly concave, for articulating with the side of the base of the 
fouith metacarpal (Plate XLI. fig. 1, m T ) ; the rest of the outer surface is very irregular, 
as if honeycombed. The distal or anterior articular surface presents a vertical median 
piominence, passing into a partly flat surface internally, and into a vertically concave 
MDCCCLIX. 5 P 
