58 
TEIITIAIIT VERTEBEATA OF THE FAYCM. 
I'liis 1)0110 differs widely from the navicular of Elephas in articulating with the 
cuboid by its outer face only, and not being interposed between that hone and the 
astragalus. From the navicular of the Aml)ly[)oda it differs mainly in the depth 
and prominence of the cctocuneiform region, which is such that the outer face of 
the navicular articulates witli the cuboid by both its upper and lower edge. In 
Uintathcrium and Conjphodou the navicular articulates with the upper edge of the 
cuboid only and the lower portion of the inner side of that bone joins the 
('ctocuneiform. It may be suggested that it is just possible that in the bone here 
described and figured the ectocuneiform may be fused with the navicular, but there 
is no actual trace of such a fusion having taken place in any specimen examined. 
Text-fig. 34. 
A. 
ast. 
Right cuboid of Arsinoitherium zitteli: A, navicular face; B, from above ; C, from below. 
ast., facet for astragalus; calc., facet for calcaneura ; nit., nit.-i, nit. 5, facets for the metatarsals ; 
nav., facets for navicular. 4 nat. size. 
The form of the bone which is regarded as the cuhoid of this animal is shown in 
text-fig. 34. The proximal surface [atit.), which artievdates with the outer third of 
the distal end ot the astragalus, is nearly fiat and almost circular in outline, only the 
navicular border being somewhat flattened. (Connected with the postero-external 
angle of the astragalar surface is a small fircet {calc.'), looking backwards, oiduvards, 
and upwards, for articulation with the calcaneum. 'I'he inner face of the bone bears 
two small facets {nav.) for union with the navicular, one on the uj)j)er border, the 
other on the lower, the two being separated by a deep groove. The distal surface' 
is gently convex ; in front it is slightly bilobate [mi. 4, mt. 5) and clearl) 
articulated with two metatarsals ; and the postero-internal angle is [eroduced into a 
blunt tuberosity. 
